#include <iostream>
#include <fstream>
#include <queue>
using namespace std;
ifstream fin("barbar.in");
ofstream fout("barbar.out");
const int Nmax=1005;
char a[Nmax][Nmax];
bool viz[Nmax][Nmax];
int n,m,k,dist[Nmax][Nmax],sol[Nmax][Nmax];
struct celula
{
    int lin,col;
};
queue<celula>q;
bool isValid(celula cell)
{
    return(cell.lin>=1 &&cell.lin<=n &&
           cell.col>=1 && cell.col<=m &&
           a[cell.lin][cell.col]!='*' &&
           viz[cell.lin][cell.col]==0 &&
           dist[cell.lin][cell.col]==-1);
}
bool isValid2(celula cell,int mid)
{
    return(cell.lin>=1 &&cell.lin<=n &&
           cell.col>=1 && cell.col<=m &&
           a[cell.lin][cell.col]!='*' &&
           sol[cell.lin][cell.col]==-1 &&
           dist[cell.lin][cell.col]>=mid);
}
void Lee()
{

    const int dx[]= {-1,0,1,0};
    const int dy[]= {0,1,0,-1};
    while(!q.empty())
    {
        celula cell=q.front();
        q.pop();
        for(int dir=0; dir<4; dir++)
        {
            celula neighbor = {cell.lin+dx[dir],cell.col+dy[dir]};
            if(isValid(neighbor))
            {
                dist[neighbor.lin][neighbor.col]=dist[cell.lin][cell.col] + 1;
                q.push(neighbor);
            }
        }
    }
}
void Lee2(celula cell,int mid)
{

    const int dx[]= {-1,0,1,0};
    const int dy[]= {0,1,0,-1};
    q.push(cell);
    while(!q.empty())
    {
        cell=q.front();
        q.pop();
        for(int dir=0; dir<4; dir++)
        {
            celula neighbor = {cell.lin+dx[dir],cell.col+dy[dir]};
            if(isValid2(neighbor,mid))
            {
                sol[neighbor.lin][neighbor.col]=sol[cell.lin][cell.col] + 1;
                q.push(neighbor);
            }
        }
    }
}
int main()
{
    celula startq,finish,start;
    fin>>n>>m;
    char x;
    for(int i=1; i<=n; i++)
    {
        for(int j=1; j<=n; j++)
        {
            dist[i][j]=-1;
            sol[i][j]=-1;
            fin>>x;
            a[i][j]=x;
            if(x=='D')
            {
                startq= {i,j};
                q.push(startq);
                dist[i][j]=0;
            }
            if(x=='O')
            {
                finish= {i,j};
            }
            if(x=='I')
            {
                start= {i,j};
                sol[i][j]=0;
            }
        }
    }
    Lee();
    /*for(int i=1;i<=n;i++)
    {
        for(int j=1;j<=n;j++)
        {
            fout<<dist[i][j]<<' ';
        }
        fout<<'\n';
    }*/
    int l=0,r=1000000,mid,solutie;
    while(l<r)
    {
        mid=(l+r)/2;
        if(mid<=dist[start.lin][start.col])
        {
            for(int i=1; i<=n; i++)
            {
                for(int j=1; j<=m; j++)
                {
                    sol[i][j]=-1;
                }
            }
            sol[start.lin][start.col]=0;
            Lee2(start,mid);
            if(sol[finish.lin][finish.col]==-1)
            {
                r=mid-1;
            }
            else
            {
                l=mid;
                solutie=mid;
            }
        }
        else
        {
            r=mid-1;
        }
    }
    fout<<solutie;
    return 0;
}