#include <fstream>
#define x first
#define y second
#define DIM 1003
using namespace std;

ifstream fin ("barbar.in");
ofstream fout("barbar.out");

char c;
pair<int, int> k[DIM*DIM],s,f;
int n,m,i,j,x,y,a[DIM][DIM],w[DIM][DIM],v[DIM][DIM],t,d,q,st,dr,mid,maxim,sol;
int di[4]={1,-1,0,0};
int dj[4]={0,0,1,-1};

int main(){
    fin>>n>>m;
    for (i=1;i<=n;i++)
        for (j=1;j<=m;j++){
            fin>>c;
            switch(c){
                case 'D': k[++d]=make_pair(i,j);break;
                case '*': w[i][j]=1;break;
                case 'I': s.x=i;s.y=j;break;
                case 'O': f.x=i;f.y=j;break;
            }
        }
    st=1;
    dr=d;
    while (st<=dr){
        if (st<=d)
            a[k[st].x][k[st].y]=1;
        for (t=0;t<4;t++){
            x=k[st].x+di[t];
            y=k[st].y+dj[t];
            if (x>0 && x<=n && y>0 && y<=m && !w[x][y] && (!a[x][y] || a[x][y]>a[k[st].x][k[st].y]+1)){
                a[x][y]=a[k[st].x][k[st].y]+1;
                k[++dr]=make_pair(x,y);
            }
        }
        st++;
    }
    for (i=1;i<=n;i++)
        for (j=1;j<=m;j++)
            maxim=max(maxim,a[i][j]);
    i=1;j=maxim;
    while (i<=j){
        mid=(i+j)/2;
        st=dr=1;
        k[st]=s;
        v[s.x][s.y]=1;
        while (st<=dr && !v[f.x][f.y]){
            for (t=0;t<4;t++){
                x=k[st].x+di[t];
                y=k[st].y+dj[t];
                if (x>0 && x<=n && y>0 && y<=m && a[x][y]>=mid && !v[x][y]){
                    v[x][y]=1;
                    k[++dr]=make_pair(x,y);
                }
            }
            st++;
        }
        if (v[f.x][f.y]){
            sol=j;
            i=mid+1;
        }
        else
            j=mid-1;
        for (int i=1;i<=n;i++)
            for (int j=1;j<=m;j++)
                v[i][j]=0;
    }
    fout<<j-1;
    fin.close();
    fout.close();
    return 0;
}