#include <fstream>
#include <queue>
#include <utility>
#include <cstring>

using namespace std;

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

const int DIM = 1010;
int n, m;
int xs, xf, ys, yf;
int a[DIM][DIM];
bool vis[DIM][DIM];
queue<pair<int, int>> q;
int di[] = { -1, 0, 1, 0 }, dj[] = { 0, 1, 0, -1 };

inline bool interior(int i, int j) {
    return i >= 1 && i <= n && j >= 1 && j <= m;
}

int binarySearch() {
    int result = -1;
    int left = 1, right = n * m;
    while (left <= right) {
        int middle = (left + right) / 2;
        if (a[xs][ys] < middle) {
            right = middle - 1;
        } else {
            memset(vis, false, sizeof(vis));
            q.push(make_pair(xs, ys));
            vis[xs][ys] = true;
            while (!q.empty()) {
                int ci = q.front().first;
                int cj = q.front().second;
                q.pop();

                for (int d = 0; d < 4; d++) {
                    int ni = ci + di[d];
                    int nj = cj + dj[d];
                    if (interior(ni, nj) && a[ni][nj] >= middle && !vis[ni][nj]) {
                        q.push(make_pair(ni, nj));
                        vis[ni][nj] = true;
                    }
                }
            }

            if (vis[xf][yf]) {
                result = middle;
                left = middle + 1;
            } else {
                right = middle - 1;
            }
        }
    }

    return result;
}

int main() {
    fin >> n >> m;
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= m; j++) {
            char ch;
            fin >> ch;

            if (ch == '*') {
                a[i][j] = -2;
            }else if (ch == '.') {
                a[i][j] = -1;
            } else if (ch == 'D') {
                q.push(make_pair(i, j));
                a[i][j] = 0;
            } else if (ch == 'I') {
                xs = i, ys = j;
                a[i][j] = -1;
            } else if (ch == 'O') {
                xf = i, yf = j;
                a[i][j] = -1;
            }
        }
    }

    while (!q.empty()) {
        int ci = q.front().first;
        int cj = q.front().second;
        q.pop();

        for (int d = 0; d < 4; d++) {
            int ni = ci + di[d];
            int nj = cj + dj[d];
            if (interior(ni, nj) && a[ni][nj] == -1) {
                q.push(make_pair(ni, nj));
                a[ni][nj] = a[ci][cj] + 1;
            }
        }
    }

    fout << binarySearch();

    return 0;
}