#include <fstream>
#include <queue>
#include <functional>
#include <algorithm>
#include <bitset>

using namespace std;

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

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

int v[1005][1005];
int n, m;

void border() {
	for (int i = 0; i <= n + 1; i++) {
		v[i][0] = -10;
		v[i][m + 1] = -10;
	}
	for (int i = 0; i <= m + 1; i++) {
		v[0][i] = -10;
		v[n + 1][i] = -10;
	}
}

int main() {
	queue<pair<int, int> > q;
	pair<int, int> enter, exit;
	char c;
	in >> n >> m;
	border();
	for (int i = 1; i <= n; i++) for (int j = 1; j <= n; j++) {
		in >> c;
		if (c == '*')
			v[i][j] = -1;
		else if (c == 'D')
			v[i][j] = -2, q.push(make_pair(i, j));
		else if (c == 'I')
			enter = make_pair(i, j);
		else if (c == 'O')
			exit = make_pair(i, j);
	}
	while (!q.empty()) {
		int x = q.front().first, y = q.front().second, val=max(0,v[x][y]);
		for (int i = 0; i < 4; i++) {
			if ((v[x + dx[i]][y + dy[i]] == 0 || v[x + dx[i]][y + dy[i]] > val + 1))
				v[x + dx[i]][y + dy[i]] = val + 1, q.push(make_pair(x + dx[i], y + dy[i]));
		}
		q.pop();
	}
	function<int(int, int)> to_v = [&](int x, int y) {
		if (x == 0 || y == 0)
			return 0;
		return (x - 1) * m + y;
	};
	function<bool(int)> cango = [&](int g) {
		int x, y;
		queue<pair<int, int> > q;
		bitset<1010025> b;
		b[0] = 1;
		q.push(enter);
		while (!q.empty()) {
			if (q.front() == exit)
				return 1;
			x = q.front().first;
			y = q.front().second;
			for (int i = 0; i < 4; i++) {
				if (!b[to_v(x + dx[i], y + dy[i])] && v[x + dx[i]][y + dy[i]] >= g) {
					q.push(make_pair(x + dx[i], y + dy[i]));
					b[to_v(x + dx[i], y + dy[i])] = 1;
				}
			}
			q.pop();
		}
		return 0;
	};
	int pos = 0;
	for (int pas = 1 << 12; pas >= 1; pas /= 2) {
		if (cango(pos + pas))
			pos += pas;
	}
	out << pos;
	return 0;
}