#include <bits/stdc++.h>
#define int long long
#pragma GCC optimize ("O3")
#define pb push_back
using namespace std;
#define f first
#define s second

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

struct cat{
    int x , y , z;
};

bool inmatt(cat a){
    if(1 <= a.x && a.x <= n && 1 <= a.y && a.y <= n && 1 <= a.z && a.z <= n)return true;
    return false;
}

bool inmat(int x, int y){
    if(1 <= x && x <= n && 1 <= y && y <= m)return true;
    return false;
}

signed main(){
    ifstream cin ("barbar.in");
    ofstream cout ("barbar.out");
    cin >> n >> m;
    vector < vector <int>> a(n + 2, vector<int>(m + 2, 1e9));
    vector <pair <int, int>> st;
    int s1, s2, e1, e2;
    for(int i=1;i <= n;i++){
        for(int j=1;j <= m;j++){
            char x;cin >> x;
            if(x == '*')a[i][j]=-1;
             else if(x == 'D'){
                st.pb({i , j});
             }else if(x == 'I'){
                s1=i, s2=j;
             }else if(x == 'O'){
                e1=i; e2=j;
             }
        }
    }
    queue<pair <int, int>> q;
    for(auto [x, y] : st){
        q.push({x, y});
        a[x][y]=0;
    }

    while(!q.empty()){
        int x=q.front().f, y=q.front().s;
        q.pop();

        for(int d=0;d < 4;d++){
            int nx=x + dx[d];
            int ny=y + dy[d];
            if(inmat(nx, ny) && a[nx][ny] != -1){
                if(a[nx][ny] > a[x][y] + 1){
                    a[nx][ny]=a[x][y] + 1;
                    q.push({nx, ny});
                }
            }
        }
    }
    
    int l=0, r=n + m;
    while(l + 1 < r){
        int mid=(l + r) / 2;
        int ok=true;
        if(a[s1][s2] < mid)ok=false;
        vector <vector <int>> vis(n + 2, vector <int> (m + 2, 0));
        q.push({s1, s2});
        while(!q.empty()){
            int x=q.front().f, y=q.front().s;
            q.pop();
            if(vis[x][y] == 1)continue;
            if(a[x][y] < mid)continue;
            vis[x][y]=1;
            for(int d=0;d < 4;d++){
                int nx=x + dx[d];
                int ny=y + dy[d];
                if(inmat(nx, ny) && a[nx][ny] != -1)q.push({nx, ny});
            }
        }
        if(vis[e1][e2] == 1)l = mid;
         else r = mid;
    }
    if(a[e1][e2] == 1e9 || l == 0)cout << "-1";
     else cout << l;
}