#include <iostream>
#include <fstream>
#include <queue>
#include <climits>

using namespace std;

const int dim = 1e3 + 5;
char a[dim][dim];
int dist[dim][dim], ddist[dim][dim];
int n, m;

struct Celula{
    int lin, col;
}start, finish;

queue <Celula> Q;

bool isValid(Celula cell){
    return (cell.lin >= 1 and cell.lin <= n and cell.col >= 1 and cell.col <= m and a[cell.lin][cell.col] != '*' and a[cell.lin][cell.col] != 'D');
}

void Lee(){
    for(int i = 1; i <= n; i++){
        for(int j = 1; j <= m; j++){
            if(a[i][j] == 'I' or a[i][j] == 'O' or a[i][j] == '.'){
                dist[i][j] = INT_MAX;
            }
            if(a[i][j] == 'D'){
                Q.push({i, j});
            }
        }
    }
    const int dx[] = {-1, 0, 1, 0};
    const int dy[] = {0, -1, 0, 1};
    while(!Q.empty()){
        Celula cell = Q.front();
        Q.pop();
        for(int dir = 0; dir < 4; dir++){
            Celula neigh = {cell.lin + dx[dir], cell.col + dy[dir]};
            if(isValid(neigh) and dist[neigh.lin][neigh.col] > dist[cell.lin][cell.col] + 1){
                dist[neigh.lin][neigh.col] = dist[cell.lin][cell.col] + 1;
                Q.push(neigh);
            }
        }
    }
}

bool Verify(int x){
    const int dx[] = {-1, 0, 1, 0};
    const int dy[] = {0, -1, 0, 1};
    for(int i = 1; i <= n; i++){
        for(int j = 1; j <= m; j++){
            ddist[i][j] = INT_MAX;
        }
    }
    Q.push(start);
    ddist[start.lin][start.col] = 0;
    while(!Q.empty()){
        Celula cell = Q.front();
        Q.pop();
        for(int dir = 0; dir < 4; dir++){
            Celula neigh = {cell.lin + dx[dir], cell.col + dy[dir]};
            if(isValid(neigh) and ddist[neigh.lin][neigh.col] > ddist[cell.lin][cell.col] + 1 and dist[neigh.lin][neigh.col] >= x){
                ddist[neigh.lin][neigh.col] = ddist[cell.lin][cell.col] + 1;
                Q.push(neigh);
            }
        }
    }
    if(ddist[finish.lin][finish.col] != INT_MAX){
        return 1;
    }
    return 0;
}

int main(){
    ifstream cin("barbar.in");
    ofstream cout("barbar.out");
    cin >> n >> m;
    for(int i = 1; i <= n; i++){
        for(int j = 1; j <= m; j++){
            cin >> a[i][j];
            if(a[i][j] == 'I'){
                start = {i, j};
            }
            if(a[i][j] == 'O'){
                finish = {i, j};
            }
        }
    }
    Lee();
    int sol = 0, left = 1, right = dist[start.lin][start.col];
    while(left <= right){
        int mid = (left + right) / 2;
        if(Verify(mid)){
            sol = mid;
            left = mid + 1;
        }
        else{
            right = mid - 1;
        }
    }
    cout << sol;
    return 0;
}