#include <iostream>
#include <fstream>
#include <queue>
#include <vector>
#include <cstring>

using namespace std;
const int nmax = 1000;

char a[nmax + 2][nmax + 2];
queue <pair <int, int> > q;
pair <int, int> aux, nou;
bool viz[nmax + 2][nmax + 2];
pair <int , int> start, finall;

int d[nmax + 2][nmax + 2];
int dx[] = {-1, 0, 1, 0};
int dy[] = {0, 1, 0, -1};

void bfs_pregen()
{
    while(!q.empty()) {
        aux = q.front();
        q.pop();
        for(int i = 0; i <= 3; ++i) {
            nou = make_pair(aux.first + dx[i], aux.second + dy[i]);
            if(a[nou.first][nou.second] != 0 && viz[nou.first][nou.second] == 0 ) {
                viz[nou.first][nou.second] = 1;
                q.push(nou);
                d[nou.first][nou.second] = d[aux.first][aux.second] + 1;
            }
        }
    }
}
void dfs(pair <int, int> x, int k) {

    viz[x.first][x.second] = 1;
    for(int i = 0; i <= 3; ++i) {
        pair <int, int> nx = make_pair(x.first + dx[i], x.second + dy[i]);
        if(d[nx.first][nx.second] >= k && a[nx.first][nx.second] != '*' && viz[nx.first][nx.second] == 0) {
            dfs(nx, k);
        }
    }
}
bool check(int k)
{
    memset(viz, 0, sizeof(viz));
    dfs(start, k);
    return viz[finall.first][finall.second];
}

int main()
{
    ifstream fin("barbar.in");
    ofstream fout("barbar.out");
    int n, m;
    int st = 0, dr, last = 0;
    fin >> n >> m;
    for(int i = 1; i <= n; ++i) {
        for(int j = 1; j <=m; ++j) {
            fin >> a[i][j];
            if(a[i][j] == 'D') {
                q.push(make_pair(i, j));
                viz[i][j] = 1;
            }
            else if(a[i][j] == '*') {
                d[i][j] = -1;
            }
            else if(a[i][j] == 'I') {
                start = make_pair(i, j);
            }
            else if(a[i][j] == 'O') {
                finall = make_pair(i, j);
            }
        }
    }
    bfs_pregen();
    for(int i = 0; i <= n + 1; ++i) {
        d[i][0] = d[i][m + 1] = -1;
    }
    for(int i = 1; i <= m; ++i) {
        d[0][i] = d[n + 1][i] = -1;
    }
    dr = n + m;
    while(st <= dr) {
        int med = (st + dr) / 2;
        if(check(med)) {
            last = med;
            st = med + 1;
        } else {
            dr = med - 1;
        }
    }
    fout << last;
    return 0;

}