#include <bits/stdc++.h>
using namespace std;
ifstream fin("barbar.in");
ofstream fout("barbar.out");
const int NMAX=1000;
int a[NMAX+5][NMAX+5];
int n, m;
int lin[]={-1, 0 , 1, 0};
int col[]={0, 1, 0 , -1};
void lee(queue<pair<int,int>> q){
    while(!q.empty()){
        int nx=q.front().first, ny=q.front().second;
        q.pop();
        for(int i=0;i<=3;i++){
            if(nx+lin[i]<=n and nx+lin[i]>=1 and ny+col[i]<=m and ny+col[i]>=1 and a[nx+lin[i]][ny+col[i]]==-1){
                a[nx+lin[i]][ny+col[i]]=a[nx][ny]+1;
                q.push({nx+lin[i], ny+col[i]});
            }
        }
    }
}
bool lee2(int x1,int x2,int y1,int y2, int val){
    int b[n+1][m+1];
    for(int i=1;i<=n;i++){
        for(int j=1;j<=m;j++){
            b[i][j]=0;
        }
    }
    queue<pair<int,int> > q;
    q.push({x1, y1});
    b[x1][y1]=1;
    while(!q.empty()){
        int nx=q.front().first;
        int ny=q.front().second;
        q.pop();
        if(nx==x2 and ny==y2){
            return true;
        }
        for(int i=0;i<=3;i++){
            if(nx+lin[i]<=n and nx+lin[i]>=1 and ny+col[i]<=m and ny+col[i]>=1 and a[nx+lin[i]][ny+col[i]]>=val and b[nx+lin[i]][ny+col[i]]==0){
                b[nx+lin[i]][ny+col[i]]=1;
                q.push({nx+lin[i], ny+col[i]});
            }
        }
    }
    return false;
}
int ans=0;
int main(){
    int x1, x2, y1, y2;
    fin>>n>>m;
    queue<pair<int,int> > q;
    for(int i=1;i<=n;i++){
        for(int j=1;j<=m;j++){
            char val;
            fin>>val;
            if(val=='.'){
                a[i][j]=-1;
            }else if(val=='*'){
                a[i][j]=-2;
            }else if(val=='D'){
                a[i][j]=0;
                q.push({i,j});
            }else if(val=='I'){
                a[i][j]=-1;
                x1=i, y1=j;
            }else if(val=='O'){
                a[i][j]=-1;
                x2=i, y2=j;
            }
        }
    }
    lee(q);
    int st=1, dr=1e6;
    while(st<=dr){
        int mij=(st+dr)/2;
        if(lee2(x1,x2,y1,y2,mij)){
            st=mij+1;
            ans=mij;
        }else{
            dr=mij-1;
        }
    }
    fout<<ans;
}