#include <fstream>
#include <queue>
using namespace std;

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

const int dim= 1e3+ 5;
string s;
char a[dim][dim];
int viz[dim][dim];
int dist[dim][dim];
int xi, yi, xj, yj;
queue <pair<int, int>> q;
int dx[10]= {0, 0, 1, -1};
int dy[10]= {-1, 1, 0, 0};
int n, m;

bool in_mat(int x, int y){
    return (1 <= x and 1 <= y and x <= n and y <= n);
}

void calc_dist(){
    while(!q.empty()){
        pair<int, int> nod= q.front();
        q.pop();

        for(int d= 0;d < 4;d++){
            int x_nou= nod.first+ dx[d];
            int y_nou= nod.second+ dy[d];
            if(viz[x_nou][y_nou]== 0 and in_mat(x_nou, y_nou)== true and (a[x_nou][y_nou] != 'D' and a[x_nou][y_nou] != '*')){
                dist[x_nou][y_nou]= 1+ dist[nod.first][nod.second];
                q.push({x_nou, y_nou});
                viz[x_nou][y_nou]= 1;
            }
        }
    }
}

void lee(int mini){
    for(int i= 1;i <= n;i++)
        for(int j= 1;j <= m;j++)
            viz[i][j]= 0;

    viz[xi][yi]= 1;
    q.push({xi, yi});
    while(!q.empty()){
        pair <int, int> nr= q.front();
        q.pop();

        for(int d= 0;d < 4;d++){
            int x= dx[d]+ nr.first;
            int y= dy[d]+ nr.second;
            if(in_mat(x, y)== true and viz[x][y]== 0 and a[x][y] != 'D' and a[x][y] != '*' and dist[x][y] >= mini){
                viz[x][y]= 1;
                q.push({x, y});
            }
        }
    }
}

int main()
{
    int i, j, x1, y1, x2, y2, x, y;
    cin >> n>> m;

    for(i= 1;i <= n;i++){
        cin >> s;
        for(j= 1;j <= m;j++){
            a[i][j]= s[j- 1];
            if(a[i][j]== 'D')
                q.push({i, j}), viz[i][j]= 1;
            if(a[i][j]== 'I')
                xi= i, yi= j;
            if(a[i][j]== 'O')
                xj= i, yj= j;
        }
    }

    calc_dist();

//    for(i= 1;i <= n;i++){
//        for(j= 1;j <= m;j++)
//            cout << dist[i][j]<<" ";
//        cout << endl;
//    }

    int st= 0, dr= n* 2, rez= 0;
    while(st <= dr){
        int mij= (st+ dr)/ 2;
        lee(mij);
        int ok= viz[xj][yj];
        if(ok== 1)
            rez= mij, st= mij+ 1;
        else dr= mij- 1;
    }
    cout << rez;


    return 0;
}