#include <iostream>
#include <fstream>
#include <deque>
#include <cstring>
#define pii pair<int, int>
#define MAX 1002
using namespace std;
int n,m,dist[MAX][MAX],v[MAX][MAX],vf[MAX][MAX];
char ch;
pii loc,com;

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

int dx[] = {-1,1,0,0};
int dy[] = {0,0,-1,1};

bool inauntru(int x, int y){
    return ((1 <= x && x <= n) && (1 <= y && y <= m));
}

bool check(int maxi){
    for(int i = 1; i <= n; i++){
        memset(vf[i], 0, sizeof(vf[i]));
    }
    deque<pii> cd;
    cd.push_back(loc);
    vf[loc.first][loc.second] = 1;
    while(!cd.empty()){
        auto [x, y] = cd.back();
        for(int k = 0; k < 4; k++){
            int xnou = x+dx[k];
            int ynou = y+dy[k];
            if(inauntru(xnou, ynou) && vf[xnou][ynou] == 0 && v[xnou][ynou] == 0 && maxi <= dist[xnou][ynou]){
                if(xnou == com.first && ynou == com.second){
                    return true;
                }
                vf[xnou][ynou] = 1;
                cd.push_front({xnou, ynou});
            }
        }
        cd.pop_back();
    }
    return false;
}

int main()
{
    deque<pii> cd;
    fin >> n >> m;
    for(int i = 1; i <= n; i++){
        for(int j = 1; j <= m; j++){
            fin >> ch;
            if(ch == 'D'){
                cd.push_back({i, j});
                dist[i][j] = 1;
            }else if(ch == 'I'){
                loc = {i, j};
            }else if(ch == '*'){
                v[i][j] = 1;
            }else if(ch == 'O'){
                com = {i, j};
            }
        }
    }
    while(!cd.empty()){
        auto [x, y] = cd.back();
        for(int k = 0; k < 4; k++){
            int xnou = x+dx[k];
            int ynou = y+dy[k];
            if(inauntru(xnou, ynou) && dist[xnou][ynou] == 0 && v[xnou][ynou] == 0){
                dist[xnou][ynou] = 1+dist[x][y];
                cd.push_front({xnou, ynou});
            }
        }
        cd.pop_back();
    }
    int ans = -1, st = 2, dr = n*m;
    while(st <= dr){
        int mid = (st+dr)/2;
        if(check(mid)){
            ans = mid;
            st = mid+1;
        }else{
            dr = mid-1;
        }
    }
    if(ans != -1){
        fout << ans-1;
    }else{
        fout << -1;
    }
    return 0;
}