#include <bits/stdc++.h>
using namespace std;

#define NMAX 1005

int n,m,mat2[NMAX][NMAX], viz[NMAX][NMAX], lg, cnt;
char mat[NMAX][NMAX];

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

pair<int,int> Q[NMAX*NMAX], Q2[NMAX*NMAX];

int sx,sy,fx,fy,lg3;
int OK(int x){
    cnt++;
    lg = 0;
    Q[++lg] = {sx,sy};
    viz[sx][sy] = cnt;
    if (mat2[sx][sy]==-1 || mat2[sx][sy] <= x + 1 || mat2[fx][fy] == -1 || mat2[fx][fy] <= x + 1) return 0;

    for (int i=1;i<=lg;i++){
        for (int k=0;k<4;k++){
            int X = Q[i].first + dx[k];
            int Y = Q[i].second + dy[k];
            if (viz[X][Y] == cnt || mat2[X][Y] == -1 || mat2[X][Y] <= x + 1) continue;
            viz[X][Y] = cnt;
            Q[++lg] = {X,Y};
            if (X == fx && Y == fy){
                return 1;
            }
        }
    }

    return 0;
}

int main()
{
    cin.sync_with_stdio(false);
    freopen("barbar.in","r",stdin);
    freopen("barbar.out","w",stdout);

    cin >> n >> m;
    for (int i=1;i<=n;i++){
        cin >> mat[i] + 1;
    }

    for (int i=1;i<=n;i++) mat2[i][0] = mat2[i][m+1] = -1;
    for (int i=1;i<=m;i++) mat2[0][i] = mat2[n+1][i] = -1;

    for (int i=1;i<=n;i++){
        for (int j=1;j<=m;j++){
            mat2[i][j] = 0;
            if (mat[i][j] == '*')
                mat2[i][j] = -1;
            else if (mat[i][j] == 'I'){
                sx = i;
                sy = j;
            }
            else if (mat[i][j] == 'O'){
                fx = i;
                fy = j;
            }
            else if (mat[i][j] == 'D'){
                Q2[++lg] = {i,j};
                mat2[i][j] = 1;
            }
        }
    }

    for (int i=1;i<=lg;i++){
        pair<int, int> crt = Q2[i];
        for (int k=0;k<4;k++){
            int X = crt.first + dx[k];
            int Y = crt.second + dy[k];
            if (mat2[X][Y] != 0) continue;
            mat2[X][Y] = mat2[crt.first][crt.second] + 1;
            Q2[++lg] = {X,Y};
        }
    }

    int st = 0, p = 1;
    for (;p<=max(n,m);p<<=1);
    for (;p>=1;p>>=1){
        if(st + p <= max(n,m) && OK(st + p))
            st += p;
    }

    if (!OK(st)){
        cout << -1 << '\n';
    }
    else{
        cout << st+1 << '\n';
    }
    return 0;
}