#include <bits/stdc++.h>
#define N 1000
#define M 1000
using namespace std;

int a[N + 1][M + 1];
const int di[] = {-1, 0, 1, 0}, dj[] = {0, 1, 0, -1}; // NESV
void BFS (queue <pair <int, int>> &Q) {
    while (!Q.empty()) {
        auto save = Q.front();
        Q.pop();

        pair <int, int> nou;
        int k;
        for (k = 0; k < 4; k++) {
            nou = {save.first + di[k], save.second + dj[k]};
            if (!a[nou.first][nou.second]) {
                a[nou.first][nou.second] = a[save.first][save.second] + 1; // a[i][j] = distanta minima de la camera {i, j} la un dragon
                Q.push(nou);
            }
        }
    }
}

int dist[N + 1][M + 1];
class heap {
public:
    int lin, col, cost;
    heap (const int &_lin, const int &_col, const int &_cost) : lin(_lin), col(_col), cost(_cost) {}
    bool operator < (const heap &x) const {
        return cost < x.cost;
    }
};

int main () {
    freopen("barbar.in", "r", stdin);
    freopen("barbar.out", "w", stdout);

    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);

    int n, m;
    cin >> n >> m;

    memset(a, 0xFF, sizeof a); // a[][] = -1
    char c;
    
    pair <int, int> start, finish;
    queue <pair <int, int>> Q;

    int i, j;
    for (i = 1; i <= n; i++)
        for (j = 1; j <= m; j++) {
            cin >> c;
            switch (c) {
            case '.':
                a[i][j] = 0;
                break;
            
            case 'I':
                a[i][j] = 0;
                start = make_pair(i, j);
                break;

            case 'D':
                a[i][j] = 0;
                Q.emplace(i, j);
                break;
            
            case 'O':
                a[i][j] = 0;
                finish = make_pair(i, j);
                break;
            }
        }

    BFS(Q);
    
    priority_queue <heap> PQ; // max heap
    PQ.emplace(start.first, start.second, a[start.first][start.second]);
    dist[start.first][start.second] = a[start.first][start.second];

    int ans = -1;
    while (!PQ.empty() && ans == -1) {
        auto save = PQ.top();
        PQ.pop();

        if (save.lin == finish.first && save.col == finish.second)
            ans = save.cost;
        else
            if (dist[save.lin][save.col] == save.cost) {
                pair <int, int> nou;
    
                int k;
                for (k = 0; k < 4; k++) {
                    nou = {save.lin + di[k], save.col + dj[k]};
                    if (a[nou.first][nou.second] != -1)
                        if (dist[nou.first][nou.second] < min(save.cost, a[nou.first][nou.second])) {
                            dist[nou.first][nou.second] = min(save.cost, a[nou.first][nou.second]);
                            PQ.emplace(nou.first, nou.second, min(save.cost, a[nou.first][nou.second]));
                        }
                }
            }
    }

    cout << ans;
    return 0;
}