#include <fstream>
using namespace std;
ifstream fin("barbar.in");
ofstream fout("barbar.out");
int i,j,x,y,q[2][1009000],u,lin,col,p,a[1002][1002],n,m,l1,l2,c1,c2,x1,y1,st,dr,mijl,cond,v[2002],ok,sol,ok1,viz[1001][1001];
char ch;
const int dx[]={-1,0,1,0};
const int dy[]={0,-1,0,1};
int main()
{
    fin>>n>>m;
    for(i=1;i<=n;i++)
        for(j=1;j<=m;j++)
        {
            fin>>ch;
            if(ch=='.')
                a[i][j]=2001;
            if(ch=='D')
            {
                q[0][++u]=i;
                q[1][u]=j;
            }
            if(ch=='O')
            {
                a[i][j]=2005;
                l2=i;
                c2=j;
            }
            if(ch=='I')
            {
                a[i][j]=2005;
                l1=i;
                c1=j;
            }
            if(ch=='*')
                a[i][j]=-2;
        }
    for(i=0;i<=n+1;i++)
    {
        a[i][0]=-10;
        a[i][m+1]=-10;
    }
    for(i=0;i<=m+1;i++)
    {
        a[0][i]=-10;
        a[n+1][i]=-10;
    }
    p=1;
    while(p<=u)
    {
        x=q[0][p];
        y=q[1][p];
        for(i=0;i<=3;i++)
        {
            x1=x+dx[i];
            y1=y+dy[i];
            if(a[x1][y1]>=0&&a[x][y]+1<a[x1][y1])
            {
                a[x1][y1]=a[x][y]+1;
                q[0][++u]=x1;
                q[1][u]=y1;
                if(a[x1][y1]>dr)
                    dr=a[x1][y1];
            }
        }
        p++;
    }
    for(i=1;i<=dr;i++)
        v[i]=i;
    st=1;
    q[0][1]=l1;
    q[1][1]=c1;
    while(st<=dr)
    {
        ok=0;
        cond=0;
        mijl=(st+dr)/2;
        p=u=1;
        if(mijl<=a[l1][c1])
        while(p<=u&&ok==0)
        {
            x=q[0][p];
            y=q[1][p];
            for(i=0;i<4;i++)
            {
                x1=x+dx[i];
                y1=y+dy[i];
                if(a[x1][y1]>=mijl&&viz[x1][y1]==0)
                {
                    q[0][++u]=x1;
                    q[1][u]=y1;
                    viz[x1][y1]=1;
                }
                if(x1==l2&&y1==c2)
                {
                    ok=1;
                    ok1=1;
                    cond=1;
                    break;
                }
            }
            p++;
        }
        if(ok==1)
        {
            sol=mijl;
            st=mijl+1;
        }
        else
            dr=mijl-1;
            for(i=1;i<=n;i++)
                for(j=1;j<=m;j++)
                viz[i][j]=0;
    }
    if(ok1==0)
        fout<<-1;
    else
        fout<<sol;

    return 0;
}