#include <bits/stdc++.h>

using namespace std;

char a[1001][1001];
int d[1001][1001], vis[1001][1001];
int xs, ys, xf, yf;
int n, m;
int dx[] = {-1, 1, 0, 0};
int dy[] = {0, 0, 1, -1};

bool inside(int x, int y) {
    return x >= 1 && x <= n && y >= 1 && y <= m;
}

bool check(int r) {
    if(d[xs][ys] < r) {
        return false;
    }
    queue<pair<int, int>> q;
    for(int i = 1; i <= n; i++) {
        for(int j = 1; j <= m; j++) {
            vis[i][j] = 0;
        }
    }
    q.push({xs, ys});
    vis[xs][ys] = 1;
    while(!q.empty()) {
        int x = q.front().first;
        int y = q.front().second;
        q.pop();
        for(int i = 0; i < 4; i++) {
            int nx = x + dx[i];
            int ny = y + dy[i];
            if(inside(nx, ny) && !vis[nx][ny] && d[nx][ny] >= r) {
                vis[nx][ny] = 1;
                q.push({nx, ny});
            }
        }
    }
    return vis[xf][yf] == 1;
}

int main() {
    ifstream cin("barbar.in");
    ofstream cout("barbar.out");
    cin >> n >> m;
    queue<pair<int, int>> q;
    for(int i = 1; i <= n; i++) {
        for(int j = 1; j <= m; j++) {
            cin >> a[i][j];
            d[i][j] = 1e9;
            if(a[i][j] == 'D') {
                d[i][j] = 0;
                q.push({i, j});
            }
            if(a[i][j] == 'I') {
                xs = i;
                ys = j;
            }
            if(a[i][j] == 'O') {
                xf = i;
                yf = j;
            }
            if(a[i][j] == '*') {
                d[i][j] = 0;
            }
        }
    }
    while(!q.empty()) {
        int x = q.front().first;
        int y = q.front().second;
        q.pop();
        for(int i = 0; i < 4; i++) {
            int nx = x + dx[i];
            int ny = y + dy[i];
            if(inside(nx, ny) && a[nx][ny] != '*' && d[nx][ny] > d[x][y] + 1) {
                d[nx][ny] = d[x][y] + 1;
                q.push({nx, ny});
            }
        }
    }
    int st = 1;
    int dr = n * m;
    int sol = 0;
    while(st <= dr) {
        int mid = (st + dr) / 2;
        if(check(mid)) {
            sol = mid;
            st = mid + 1;
        } else {
            dr = mid - 1;
        }
    }
    cout << sol;
    return 0;
}