#include <iostream>
#include <cstring>
#include <fstream>
#define MAX 1002
using namespace std;
int n,m,v[MAX][MAX],d[MAX][MAX],px,py,ox,oy,p,u;
bool viz[MAX][MAX];
int dx[]={-1,0,1,0},dy[]={0,1,0,-1};

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

struct dragon{
    int x, y;
} q[MAX*MAX];

bool inauntru(int l, int c){
    return (l >= 1 && l <= n) && (c >= 1 && c <= m);
}

bool lee(int x){
    memset(viz, 0, sizeof(viz));
    int p=1,u=1;
    if(d[px][py] < x){
        return 0;
    }
    q[u] = {px, py}; viz[px][py] = 1;
    while(p <= u){
        int drx = q[p].x;
        int dry = q[p].y;
        for(int i = 0; i < 4; i++){
            int lv = drx+dx[i];
            int cv = dry+dy[i];
            if(v[lv][cv] == 0 && viz[lv][cv] == 0 && inauntru(lv, cv) && d[lv][cv] >= x){
                viz[lv][cv] = 1;
                q[++u] = {lv, cv};
                if(lv == ox && cv == oy){
                    return 1;
                }
            }
        }
        p++;
    }
    return 0;
}

int main()
{
    fin >> n >> m;
    for(int i = 1; i <= n; i++){
        for(int j = 1; j <= m; j++){
            char ch;
            fin >> ch;
            /// D - 1
            /// I - 2
            /// * - 3
            if(ch == '*'){
                v[i][j] = 1;
            }else if(ch == 'I'){
                px = i,py = j;
            }else if(ch == 'O'){
                ox = i,oy = j;
            }else if(ch == 'D'){
                /// adaug in coada dragonul
                viz[i][j] = 1;
                q[++u] = {i, j};
            }
        }
    }
    p = 1;
    while(p <= u){
        int drx = q[p].x;
        int dry = q[p].y;
        for(int i = 0; i < 4; i++){
            int lv = drx+dx[i];
            int cv = dry+dy[i];
            if(viz[lv][cv] == 0 && v[lv][cv] == 0 && inauntru(lv, cv)){
                d[lv][cv] = d[drx][dry]+1;
                viz[lv][cv] = 1;
                q[++u] = {lv, cv};
            }
        }
        p++;
    }
    int st = 1, dr = max(n, m);
    int sol = -1;
    while(st <= dr){
        int mid = (st+dr)/2;
        bool ok = lee(mid);
        if(ok == 1){
            sol = mid;
            st = mid+1;
        }else{
            dr = mid-1;
        }
    }
    fout << sol << "\n";
    return 0;
}