#include <iostream>
#include <fstream>
#include <queue>
#include <vector>
using namespace std;

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

struct Waypoint {
    int x, y, d;
};

struct Cell {
    int x, y;
};

int dx[4] = {-1, 0, 1, 0};
int dy[4] = {0, 1, 0, -1};

int r, c;
Cell start, ex;
int dist[1001][1001], best[1001][1001];
bool pushed[1001][1001];
char a[1001][1001];
queue<Cell> q;


void calculate_distances() {
    while (!q.empty()) {
        Cell w = q.front(); q.pop();
        int x = w.x, y = w.y;
        for (int k = 0; k < 4; ++k) {
            int i = x + dx[k];
            int j = y + dy[k];
            if (i >= 1 && i <= r && j >= 1 && j <= c) {
                if ((a[i][j] == '.' || a[i][j] == 'I' || a[i][j] == 'O') && dist[i][j] == 0) {
                    dist[i][j] = dist[x][y] + 1;
                    q.push({i, j});
                }
            }
        }
    }
}


bool solve(int x, int y, int min_dist) {
    if (x == ex.x && y == ex.y) {
        return true;
    }
    pushed[x][y] = true;
    bool reached = false;


    for (int k = 0; k < 4; ++k) {
        int i = x + dx[k];
        int j = y + dy[k];
        if (i >= 1 && i <= r && j >= 1 && j <= c) {
            if (!pushed[i][j] && dist[i][j] >= min_dist) {
                reached = solve(i, j, min_dist);
                if (reached) {
                    break;
                }
            }
        }
    }

    pushed[x][y] = false;
    return reached;
}


int main()
{
    in >> r >> c;
    for (int i = 1; i <= r; ++i) {
        for (int j = 1; j <= c; ++j) {
            in >> a[i][j];
            if (a[i][j] == 'I') {
                start = {i, j};
            } else if (a[i][j] == 'O') {
                ex = {i, j};
            } else if (a[i][j] == 'D') {
                q.push({i, j});
            }
        }
    }

    calculate_distances();

    int sol = 0;
    int left = 1, right = r * c, mid;

    while (left != right) {
        mid = (left + right) / 2;
        if (solve(start.x, start.y, mid)) {
            left = mid + 1;
            sol = mid;
        } else {
            right = mid;
        }
    }


    if (sol == 0) out << -1; else out << sol;




    return 0;
}