#include <fstream>
#include <cstdio>
#include <math.h>
#include <algorithm>
#include <queue>

using namespace std;
#define llu long long unsigned
#define ll long long
#define pb push_back
#define mp make_pair

const int N = 1005;
char h[N][N];
int danger[N][N], dp[N][N];
queue < pair<int, int> > q;
int d[4][2] = {
    {-1, 0}, {1, 0}, {0, -1}, {0, 1}
};

void go(int xS, int yS){
    int x, y, nx, ny, i;
    q.push({xS, yS});
    while(q.empty() == false){
        x = q.front().first;
        y = q.front().second;
        q.pop();
        for(i = 0;i < 4;i++){
            nx = x + d[i][0];
            ny = y + d[i][1];
            if(dp[nx][ny] == 1e9 && h[nx][ny] != '*'){
                dp[nx][ny] = min(dp[x][y], danger[nx][ny]);
                q.push({nx, ny});
            }else if(min(dp[x][y], danger[nx][ny]) > dp[nx][ny] && h[nx][ny] != '*'){
                dp[nx][ny] = min(dp[x][y], danger[nx][ny]);
                q.push({nx, ny});
            }
        }
    }
}

int main(){
    int n, m, i, j, x, y, nx, ny, xS, yS, xF, yF;
    freopen("barbar.in", "r", stdin);
    freopen("barbar.out", "w", stdout);
    scanf("%d %d", &n, &m);
    for(i = 1;i <= n;i++){
        scanf("%s", h[i]+1);
    }
    for(i = 0;i <= n+1;i++){
        h[i][0] = h[i][m+1] = '*';
    }
    for(i = 0;i <= m+1;i++){
        h[0][i] = h[n+1][i] = '*';
    }
    for(i = 1;i <= n;i++){
        for(j = 1;j <= m;j++){
            danger[i][j] = -1;
            dp[i][j] = 1e9;
            if(h[i][j] == 'D'){
                q.push({i, j});
                danger[i][j] = 0;
            }else if(h[i][j] == 'I'){
                xS = i;
                yS = j;
            }else if(h[i][j] == 'O'){
                xF = i;
                yF = j;
            }
        }
    }
    while(q.empty() == false){
        x = q.front().first;
        y = q.front().second;
        q.pop();
        for(i = 0;i < 4;i++){
            nx = x + d[i][0];
            ny = y + d[i][1];
            if(danger[nx][ny] == -1 && h[nx][ny] != '*'){
                danger[nx][ny] = danger[x][y] + 1;
                q.push({nx, ny});
            }
        }
    }
    dp[xS][yS] = danger[xS][yS];
    go(xS, yS);
    if(dp[xF][yF] != 1e9){
        printf("%d",dp[xF][yF]);
    }else{
        printf("-1");
    }
    return 0;
}