#include "bits/stdc++.h"
#define pii std :: pair < int, int >

const int NMAX = 1000;

int dx[] = {0, 0, -1, 1};
int dy[] = {-1, 1, 0, 0};

int n, m, dist[NMAX + 5][NMAX + 5], x_start, y_start, x_stop, y_stop, maxx, sol;
int d[NMAX + 5][NMAX + 5];
char mat[NMAX + 5][NMAX + 5];

bool InMat(int i, int j){
    if(i >= 1 and i <= n and j >= 1 and j <= m){
        return true;
    }
    return false;
}

std :: queue < pii > q;

void BFS_Dragons(){
    while(!q.empty()){
        pii node = q.front();
        q.pop();
        for(int k = 0; k < 4; k++){
            int new_line = node.first + dx[k];
            int new_column = node.second + dy[k];
            if(InMat(new_line, new_column) and dist[new_line][new_column] == -1 and (mat[new_line][new_column] == '.' or mat[new_line][new_column] == 'O')){
                dist[new_line][new_column] = dist[node.first][node.second] + 1;
                q.push({new_line, new_column});
            }
        }
    }
}
bool Check(int x){


    for(int i = 1; i <= n; i++){
        for(int j = 1; j <= m; j++){
            d[i][j] = -1;
        }
    }

    while(!q.empty()){
        q.pop();
    }

    q.push({x_start, y_start});
    while(!q.empty()){
        auto node = q.front();
        q.pop();
        for(int k = 0; k < 4; k++){
            int new_line = node.first + dx[k], new_column = node.second + dy[k];

            if(new_line == x_stop and new_column == y_stop){
                return true;
            }

            if(InMat(new_line, new_column) and d[new_line][new_column] == -1 and dist[new_line][new_column] >= x){
                d[new_line][new_column] = d[node.first][node.second] + 1;
                q.push({new_line, new_column});
            }
        }
    }
    return false;
}

void Solve(){
    std :: cin >> n >> m;

    for(int i = 1; i <= n; i++){
        for(int j = 1; j <= m; j++){
            dist[i][j] = -1;
        }
    }

    for(int i = 1; i <= n; i++){
        for(int j = 1; j <= m; j++){
            std :: cin >> mat[i][j];
            if(mat[i][j] == 'D'){
                dist[i][j] = 0;
                q.push({i, j});
            }else if(mat[i][j] == 'O'){
                x_stop = i, y_stop = j;
            }else if(mat[i][j] == 'I'){
                x_start = i, y_start = j;
            }
        }
    }

    BFS_Dragons();

    for(int i = 1; i <= n; i++){
        for(int j = 1; j <= m; j++){
            maxx = std :: max(dist[i][j], maxx);
        }
        //std :: cout << '\n';
    }

    //std :: cout << Check(2) << '\n';
    int left = 0, right = maxx;
    while(left <= right){
        int mid = (left + right) >> 1;
        if(Check(mid)){
            left = mid + 1;
            sol = mid;
        }else{
            right = mid - 1;
        }
    }

    std :: cout << sol;


}

signed main(){
    std :: ios_base :: sync_with_stdio(false);
    std :: cin.tie(nullptr);

    freopen("barbar.in", "r", stdin);
    freopen("barbar.out", "w", stdout);

    Solve();

    return 0;
}