//ALEXANDRU MICLEA

#include <vector>
#include <algorithm>
#include <string>
#include <queue>
#include <map>
#include <set>
#include <unordered_map>
#include <time.h>
#include <iomanip>
#include <deque>
#include <math.h>
#include <cmath>
#include <assert.h>
#include <stack>
#include <bitset>
#include <random>
#include <chrono>

using namespace std;

#include <fstream>
ifstream cin("barbar.in"); ofstream cout("barbar.out");
int m, n;
int dx[4] = { -1,1,0,0 };
int dy[4] = { 0,0,1,-1 };
int obst[1005][1005];
int dist[1005][1005];
int used[1005][1005];
char c;
pair <int, int> I, O;
queue <pair<int, int>> q;

void dragon() {
	while (!q.empty()) {
		pair<int, int> now = q.front();
		q.pop();

		for (int i = 0; i <= 3; i++) {
			int x = now.first + dx[i];
			int y = now.second + dy[i];

			if (x < 1 || y < 1 || x > m || y > n) {
				continue;
			}

			if (obst[x][y]) {
				continue;
			}

			if (dist[x][y] <= dist[now.first][now.second] + 1) {
				continue;
			}
			dist[x][y] = dist[now.first][now.second] + 1;
			q.push({ x,y });
		}
	}

	//DEBUG
	for (int i = 1; i <= m; i++) {
		for (int j = 1; j <= n; j++) {
			cout << dist[i][j] << " ";
		}
		cout << '\n';
	}
}

void lee(int cap) {
	while (!q.empty()) {
		pair<int, int> now = q.front();
		q.pop();

		for (int i = 1; i <= 3; i++) {
			int x = now.first + dx[i];
			int y = now.second + dy[i];

			if (x < 1 || y < 1 || x > m || y > n) {
				continue;
			}

			if (obst[x][y]) {
				continue;
			}

			if (used[x][y]) {
				continue;
			}

			if (dist[x][y] < cap) {
				continue;
			}

			used[x][y] = 1;
			q.push({ x,y });
		}
	}
}

void rezolvare() {
	int ans = 0;
	int st = 1;
	int dr = dist[I.first][I.second];
	while (st <= dr) {
		int mid = (st + dr) / 2;
		used[I.first][I.second] = 1;
		q.push(I);
		lee(mid);
		if(used[O.first][O.second]){
			st = mid + 1;
			ans = mid;
		}
		else {
			dr = mid - 1;
		}

		for (int i = 1; i <= m; i++) {
			for (int j = 1; j <= n; j++) {
				used[i][j] = 0;
			}
		}
	}

	cout << ans;
}


int main() {

	cin >> m >> n;
	for (int i = 1; i <= m; i++) {
		for (int j = 1; j <= n; j++) {
			cin >> c;
			dist[i][j] = 1e9;
			if (c == '*') {
				obst[m][n] = 1;
			}
			if (c == 'D') {
				q.push({ m, n });
				dist[i][j] = 0;
			}
			if (c == 'I') {
				I = { m, n };
			}
			if (c == 'O') {
				O = { m, n };
			}
		}
	}

	dragon();
	rezolvare();

	return 0;
}