#include <iostream>
#include <queue>
#include <algorithm>
#include <vector>

#define NMAX 1000

using namespace std;
FILE *fin, *fout ;


struct elem {
  int x ;
  int y ;
};

char mat [ NMAX + 1 ] [ NMAX + 1 ] ;
int distDr [ NMAX + 1 ] [ NMAX + 1 ] ;
int dist [ NMAX + 1 ] [ NMAX + 1 ] ;
int dirl [ 4 ] = {0, 1, 0, -1 } ;
int dirc [ 4 ] = {1, 0, -1, 0 } ;
vector <elem> drag ;
queue <elem> q ;

void initdist (int n, int m) {
  int i, j ;
  for (i = 0 ; i < n+1 ; i++ ) {
    for (j = 0 ; j < n+1 ; j++ ) {
      dist[i][j] = 0 ;
    }
  }
}

void bfsdrag (int n, int m) {
  int i ;
  for (i = 0 ; i < drag.size() ; i++ )
    q.push({drag[i].x, drag[i].y}) ;
  while (!q.empty()) {
    for (int dir = 0 ; dir < 4 ; dir++ ) {
      int frx = q.front().x + dirl[dir] ;
      int fry = q.front().y + dirc[dir] ;
      if ( (mat[frx][fry] == '.' || mat[frx][fry] == 'O' ) && distDr[frx][fry] == 0 ) {
        distDr[frx][fry] = distDr[q.front().x][q.front().y] + 1 ;
        q.push({frx, fry}) ;
      }
    }
    q.pop() ;
  }
}

void bfs (int n, int m, int xst, int yst, int val ) {
  q.push({xst, yst}) ;
  while (!q.empty()) {
    for (int dir = 0 ; dir < 4 ; dir++ ) {
      int frx = q.front().x + dirl[dir] ;
      int fry = q.front().y + dirc[dir] ;
      if ( (mat[frx][fry] == '.' || mat[frx][fry] == 'O' ) && dist[frx][fry] == 0 && distDr[frx][fry] >= val ) {
        dist[frx][fry] = dist[q.front().x][q.front().y] + 1 ;
        q.push({frx, fry}) ;
      }
    }
    q.pop() ;
  }
}

char verif (int n, int m, int xf, int yf, int xst, int yst, int val ) {
  bfs(n, m, xst, yst, val) ;
  //for (int i = 1 ; i <= n ; i++ ) {
  //  for (int j = 1 ; j <= m ; j++ ) {
  //    fprintf (fout, "%d ", dist[i][j] ) ;
  //  }
   // fprintf (fout, "\n" ) ;
  //}
 // fprintf (fout, "\n\n\n" ) ;
  if (dist[xf][yf] != 0 ) {
    initdist(n, m) ;
    return 1 ;
  }
  initdist(n, m) ;
  return 0 ;
}

int main() {
  fin = fopen ("barbar.in", "r" ) ;
  fout = fopen ("barbar.out", "w" ) ;
  int n, i, m, xst, yst, xf, yf, st, dr, mid, j ;
  char c ;
  fscanf (fin, "%d%d\n", &n, &m ) ;
  for (i = 1 ; i <= n ; i++ ) {
    for (j = 1 ; j <= m ; j++ ) {
      c = fgetc(fin) ;
      switch (c) {
        case 'O' : {
          xf = i ;
          yf = j ;
          break ;
        }
        case 'I' : {
          xst = i ;
          yst = j ;
          break ;
        }
        case 'D' : {
          drag.push_back({i, j}) ;
          break ;
        }
      }
      mat[i][j] = c ;
    }
    c = fgetc(fin) ; /// enter
  }
  bfsdrag(n, m) ;
  st = 1 ;
  dr = max (n, m) ;
  while (st <= dr) {
    mid = (st + dr) / 2 ;
    if (verif(n, m, xf, yf, xst, yst, mid) == 1 )
      st = mid + 1 ;
    else
      dr = mid - 1 ;
  }
  fprintf (fout, "%d", dr ) ;
  return 0;
}