#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;
}