#include <fstream>
#include <algorithm>
#include <cstring>
#include <vector>
#include <climits>
#include <iostream>
using namespace std;

const int MAXN = 1005;
int n, m;
int v[MAXN][MAXN], a[MAXN][MAXN];
char s[MAXN];
int xi, yi, xf, yf;
vector<int> c[3];
int drx[4] = {-1, 0, 1, 0};
int dry[4] = {0, 1, 0, -1};

void border() {
    for (int i = 0; i <= m + 1; i++) {
        v[i][0] = -1;
        v[i][n + 1] = -1;
    }
    for (int i = 0; i <= n + 1; i++) {
        v[0][i] = -1;
        v[m + 1][i] = -1;
    }
}

int main() {
    ifstream f("barbar.in");
    ofstream g("barbar.out");
    f >> m >> n;
    for (int i = 1; i <= m; i++) {
        f >> s;
        for (int j = 0; j < n; j++) {
            if (s[j] == '*') {
                v[i][j + 1] = -1;
            }
            else if (s[j] == 'D') {
                v[i][j + 1] = -1;
                c[1].push_back(i);
                c[2].push_back(j + 1);
            }
            else if (s[j] == 'I') {
                xi = i;
                yi = j + 1;
            }
            else if (s[j] == 'O') {
                xf = i;
                yf = j + 1;
            }
        }
    }
    border();
    int ci = 0;
    while (ci < c[1].size()) {
        int x = c[1][ci];
        int y = c[2][ci];
        for (int k = 0; k < 4; ++k) {
            int lin = x + drx[k];
            int col = y + dry[k];
            if (a[lin][col] == 0 && v[lin][col] != -1) {
                a[lin][col] = a[x][y] + 1;
                c[1].push_back(lin);
                c[2].push_back(col);
            }
        }
        ci++;
    }


    int st = 1;
    int dr = MAXN +2;
    int sol = -1;
    while (st <= dr) {
        int mid = (st + dr) / 2;
        for (int i = 1; i <= m; ++i) {
            for (int j = 1; j <= n; ++j) {
                if (v[i][j] != -1) {
                    v[i][j] = 0;
                }
            }
        }
        if (a[xi][yi] >= mid) {
            c[1].clear();
            c[2].clear();
            ci = 0;
            c[1].push_back(xi);
            c[2].push_back(yi);
            v[xi][yi] = 1;
            while (ci < c[1].size()) {
                int x = c[1][ci];
                int y = c[2][ci];
                for (int k = 0; k < 4; k++) {
                    int lin = x + drx[k];
                    int col = y + dry[k];
                    if (v[lin][col] == 0 && (a[lin][col] >= mid || a[lin][col] == 0)) {
                        v[lin][col] = v[x][y] + 1;
                        c[1].push_back(lin);
                        c[2].push_back(col);
                    }
                }
                ci++;
            }
        }
        if (v[xf][yf] > 0) {
            sol = mid;
            st = mid + 1;
        }
        else {
            dr = mid - 1;
        }
    }
    g << sol;
    return 0;
}