#include <fstream>
#include <queue>

using namespace std;

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

int n, m;
pair <int, int> a, b;

queue <pair <int, int>> q;
char v[1005][1005];
bool viz[1005][1005];
int dist[1005][1005], dp[1005][1005];
int dx[] = {-1, 0, 1, 0};
int dy[] = {0, 1, 0, -1};

bool check(int val) {
  q.push({a.first, a.second});
  for(int i = 1; i <= n; i++) {
    for(int j = 1; j <= m; j++)
      viz[i][j] = 0;
  }
  if(dist[a.first][a.second] < val)
    return 0;
  viz[a.first][a.second] = 1;
  while(!q.empty()) {
    pair <int, int> nod = q.front();
    q.pop();
    for(int i = 0; i < 4; i++) {
      int x = nod.first + dx[i], y = nod.second + dy[i];
      if(v[x][y] != '*' && 1 <= x && x <= n && 1 <= y && y <= m && !viz[x][y] && dist[x][y] >= val)
        q.push({x, y}), viz[x][y] = 1;
    }
  }
  return viz[b.first][b.second];
}

int main() {
  cin >> n >> m;
  for(int i = 1; i <= n; i++) {
    cin >> (v[i] + 1);
    for(int j = 1; j <= m; j++) {
      if(v[i][j] == 'D')
        q.push({i, j}), dist[i][j] = 0;
      else
        dist[i][j] = n * m + 5;
    }
  }
  while(!q.empty()) {
    pair <int, int> nod = q.front();
    q.pop();
    for(int i = 0; i < 4; i++) {
      int x = nod.first + dx[i], y = nod.second + dy[i];
      if(v[x][y] != '*' && 1 <= x && x <= n && 1 <= y && y <= m && dist[x][y] > dist[nod.first][nod.second] + 1) {
        dist[x][y] = dist[nod.first][nod.second] + 1;
        q.push({x, y});
      }
    }
  }
  for(int i = 1; i <= n; i++) {
    for(int j = 1; j <= m; j++) {
      dist[i][j] = (dist[i][j] == n * m + 5 ? 0 : dist[i][j]);
      if(v[i][j] == 'I')
        a = {i, j};
      if(v[i][j] == 'O')
        b = {i, j};
    }
  }
  int st = 1, dr = n + m, mid;
  while(st <= dr) {
    mid = (st + dr) >> 1;
    if(!check(mid))
      dr = mid - 1;
    else
      st = mid + 1;
  }
  if(dr)
    cout << dr;
  else
    cout << -1;
  return 0;
}