#include <bits/stdc++.h>
#define NMAX 1000

using namespace std;

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

int n, m, xi, yi, xo, yo, dist[NMAX + 2][NMAX + 2], tr[NMAX + 2][NMAX + 2], cnt;
int st, dr, mij, ans = INT_MAX;
char mat[NMAX + 2][NMAX + 2];

int dx[4] = {-1, 1, 0, 0};
int dy[4] = {0, 0, -1, 1};
queue<pair<int, int>> qd;

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

int main()
{
    fin >> n >> m;
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= m; j++) {
            fin >> mat[i][j];
            dist[i][j] = INT_MAX;
            if (mat[i][j] == 'I') {
                xi = i;
                yi = j;
            }
            if (mat[i][j] == 'O') {
                xo = i;
                yo = j;
            }
            if (mat[i][j] == 'D') {
                qd.push({i, j});
                dist[i][j] = 0;
            }
        }
    }

    while (!qd.empty()) {
        int lin = qd.front().first;
        int col = qd.front().second;
        qd.pop();
        for (int dir = 0; dir < 4; dir++) {
            int newlin = lin + dx[dir];
            int newcol = col + dy[dir];
            if (inmat(newlin, newcol) && mat[newlin][newcol] != '*' && dist[lin][col] + 1 < dist[newlin][newcol]) {
                dist[newlin][newcol] = dist[lin][col] + 1;
                qd.push({newlin, newcol});
            }
        }
    }

    st = 1, dr = (NMAX + 2) * (NMAX + 2);
    while (st <= dr) {
        mij = (st + dr) >> 1;
        cnt++;
        if (mij <= dist[xi][yi]) {
            queue<pair<int, int>> q;
            q.push({xi, yi});
            tr[xi][yi] = cnt;

            while (!q.empty()) {
                int lin = q.front().first;
                int col = q.front().second;
                q.pop();
                for (int dir = 0; dir < 4; dir++) {
                    int newlin = lin + dx[dir];
                    int newcol = col + dy[dir];
                    if (inmat(newlin, newcol) && mat[newlin][newcol] != '*' && mat[newlin][newcol] != 'D' && mij <= dist[newlin][newcol] && tr[newlin][newcol] != cnt) {
                        tr[newlin][newcol] = cnt;
                        q.push({newlin, newcol});
                    }
                }
            }
        }
        if (tr[xo][yo] == cnt) {
            ans = mij;
            st = mij + 1;
        }
        else {
            dr = mij - 1;
        }
    }
    if (ans != INT_MAX) {
        fout << ans;
    }
    else {
        fout << -1;
    }
    return 0;
}