#define _GLIBCXX_FILESYSTEM
#include <bits/stdc++.h>
using namespace std;
#define endl '\n'

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

const int MX_SZ = 1005;
const int INF = 1<<30;
const int DX[4] = {-1, 0, 1,  0};
const int DY[4] = { 0, 1, 0, -1};

struct xy{
  int x,y;
};

int N,M,d[MX_SZ][MX_SZ],l=INF,r,ans;
char m[MX_SZ][MX_SZ];
xy st, en;
queue<xy> q;
bitset <MX_SZ> bs[MX_SZ];

void reset(){
  for(int i = 1; i <= N; ++i)
    for(int j = 1; j <= M; ++j)
      bs[i][j] = 0;
}

void read(){
  fin>>N>>M;
  for(int i = 1; i <= N; ++i)
    for(int j = 1; j <= M; ++j){
      fin>>m[i][j];
      d[i][j] = INF;
      if(m[i][j] == 'I') st = {i, j};
      else if(m[i][j] == 'D') q.push({i, j}), d[i][j] = 0;
      else if(m[i][j] == 'O') en = {i, j};
    }
}

bool bfs(const int &p){
  reset();
  q.push(st);
  bs[st.x][st.y] = 1;

  if(d[st.x][st.y] < p) return 0;

  while(!q.empty()){
    xy f = q.front();
    q.pop();

    for(int i = 0; i < 4; ++i){
      xy nx = {f.x + DX[i], f.y + DY[i]};
      if((m[nx.x][nx.y] == '.' || m[nx.x][nx.y] == 'O') && d[nx.x][nx.y] >= p && bs[nx.x][nx.y] == 0){
        bs[nx.x][nx.y] = 1;
        q.push(nx);
      }
    }
  }

  return bs[en.x][en.y] == 1 ? 1 : 0;
}

int main(){
  ios::sync_with_stdio(0);
  read();

  for(int i = 0; i <= M + 1; ++i)
    m[0][i] = m[N + 1][0] = '*';

  for(int i = 0; i <= N + 1; ++i)
    m[i][0] = m[0][M + 1] = '*';

  while(!q.empty()){
    xy f = q.front();
    q.pop();

    for(int i = 0; i < 4; ++i){
      xy nx = {f.x + DX[i], f.y + DY[i]};
      if(d[nx.x][nx.y] > d[f.x][f.y] + 1 && m[nx.x][nx.y] != '*'){
        d[nx.x][nx.y] = d[f.x][f.y] + 1;
        r = max(r, d[nx.x][nx.y]);
        l = min(l, d[nx.x][nx.y]);
        q.push(nx);
      }
    }
  }

  while(l <= r){
    int m = (l + r) / 2;

    if(bfs(m)){
      ans = max(ans, m);
      ++l;
    }
    else{
      --r;
    }
  }

  fout<<(ans?ans:-1);
}