#include <fstream>
#include <queue>
using namespace std;
ifstream f("barbar.in");
ofstream g("barbar.out");
int R,C;
int Matrix[1005][1005],DP[1005][1005],Counter[1005][1005];
int Aux[1005][1005];
bool Yes[1005][1005];
queue <int> Line;
queue <int> Col;
int X1,Y1,X2,Y2;
void Read()
{
    int i,j;
    int ident=1;
    f>>R>>C;
    for(i=1;i<=R;i++)
        for(j=1;j<=C;j++)
        {
            char value;
            f>>value;
            if(value=='*')
                Matrix[i][j]=-1;
            if(value=='I')
                X1=i,Y1=j;
            if(value=='O')
                X2=i,Y2=j;
            if(value=='D')
            {
                Line.push(i);
                Col.push(j);
                Yes[i][j]=1;
                Aux[i][j]=ident;
                ident++;
            }
        }
    for(i=0;i<=R+1;i++)
        Matrix[i][0]=Matrix[i][C+1]=-1;
    for(i=0;i<=C+1;i++)
        Matrix[0][i]=Matrix[R+1][i]=-1;
}
void Browse()
{
    while(!Line.empty())
    {
        int x=Line.front();
        int y=Col.front();
        Yes[x][y]=0;
        Line.pop();
        Col.pop();
        if(Aux[x+1][y]==0 && Matrix[x+1][y]!=-1)
        {
            Matrix[x+1][y]=Matrix[x][y]+1;
            Line.push(x+1);
            Col.push(y);
            Yes[x+1][y]=1;
            Aux[x+1][y]=Aux[x][y];
        }
        else
        {
            if(Matrix[x+1][y]!=-1)
            {
                if(Matrix[x+1][y]>Matrix[x][y]+1)
                {
                    Matrix[x+1][y]=Matrix[x][y]+1;
                    if(Yes[x+1][y]==0)
                    {
                        Line.push(x+1);
                        Col.push(y);
                        Yes[x+1][y]=1;
                    }
                }
            }
        }
        if(Aux[x-1][y]==0 && Matrix[x-1][y]!=-1)
        {
            Matrix[x-1][y]=Matrix[x][y]+1;
            Line.push(x-1);
            Col.push(y);
            Yes[x-1][y]=1;
            Aux[x-1][y]=Aux[x][y];
        }
        else
        {
            if(Matrix[x-1][y]!=-1)
            {
                if(Matrix[x-1][y]>Matrix[x][y]+1)
                {
                    Matrix[x-1][y]=Matrix[x][y]+1;
                    if(Yes[x-1][y]==0)
                    {
                        Line.push(x-1);
                        Col.push(y);
                        Yes[x-1][y]=1;
                    }
                }
            }
        }
        if(Aux[x][y-1]==0 && Matrix[x][y-1]!=-1)
        {
            Matrix[x][y-1]=Matrix[x][y]+1;
            Line.push(x);
            Col.push(y-1);
            Yes[x][y-1]=1;
            Aux[x][y-1]=Aux[x][y];
        }
        else
        {
            if(Matrix[x][y-1]!=-1)
            {
                if(Matrix[x][y-1]>Matrix[x][y]+1)
                {
                    Matrix[x][y-1]=Matrix[x][y]+1;
                    if(Yes[x][y-1]==0)
                    {
                        Line.push(x);
                        Col.push(y-1);
                        Yes[x][y-1]=1;
                    }
                }
            }
        }
        if(Aux[x][y+1]==0 && Matrix[x][y+1]!=-1)
        {
            Matrix[x][y+1]=Matrix[x][y]+1;
            Line.push(x);
            Col.push(y+1);
            Yes[x][y+1]=1;
            Aux[x][y+1]=Aux[x][y];
        }
        else
        {
            if(Matrix[x][y+1]!=-1)
            {
                if(Matrix[x][y+1]>Matrix[x][y]+1)
                {
                    Matrix[x][y+1]=Matrix[x][y]+1;
                    if(Yes[x][y+1]==0)
                    {
                        Line.push(x);
                        Col.push(y+1);
                        Yes[x][y+1]=1;
                    }
                }
            }
        }
    }
}
bool Solve(int value)
{
    Line.push(X1);
    Col.push(Y1);
    while(!Line.empty())
    {
        int x=Line.front();
        int y=Col.front();
        Line.pop();
        Col.pop();
        if(x==X2 && y==Y2)
            return 1;
        if(Matrix[x+1][y]!=-1 && Matrix[x+1][y]>=value)
        {
            if(Yes[x+1][y]==0)
            {
                Line.push(x+1);
                Col.push(y);
                Yes[x+1][y]=1;
            }
        }
        if(Matrix[x-1][y]!=-1 && Matrix[x-1][y]>=value)
        {
            if(Yes[x-1][y]==0)
            {
                Line.push(x-1);
                Col.push(y);
                Yes[x-1][y]=1;
            }
        }
        if(Matrix[x][y-1]!=-1 && Matrix[x][y-1]>=value)
        {
            if(Yes[x][y-1]==0)
            {
                Line.push(x);
                Col.push(y-1);
                Yes[x][y-1]=1;
            }
        }
        if(Matrix[x][y+1]!=-1 && Matrix[x][y+1]>=value)
        {
            if(Yes[x][y+1]==0)
            {
                Line.push(x);
                Col.push(y+1);
                Yes[x][y+1]=1;
            }
        }
    }
    return 0;
}
void Binary_Search()
{
    int st=1,dr=min(Matrix[X1][Y1],Matrix[X2][Y2]),mid,sol;
    while(st<=dr)
    {
        mid=(st+dr)/2;
        for(int i=1;i<=R;i++)
            for(int j=1;j<=C;j++)
                Yes[i][j]=0;
        while(!Line.empty())
        {
            Line.pop();
            Col.pop();
        }
        if(Solve(mid)==1)
        {
            sol=mid;
            st=mid+1;
        }
        else
            dr=mid-1;
    }
    g<<sol<<"\n";
}
int main()
{
    Read();
    Browse();
    Binary_Search();
    return 0;
}