#include <bits/stdc++.h>

using namespace std;

inline void Open(const string Name) {
    #ifndef ONLINE_JUDGE
        (void)!freopen((Name + ".in").c_str(), "r", stdin);
        (void)!freopen((Name + ".out").c_str(), "w", stdout);
    #endif
}

const int l[] = {-1, 1, 0, 0}, c[] = {0, 0, -1, 1};

queue <array <int, 2>> q;

char ch;

int a[1002][1002], b[1002][1002];
int N, M, xi, yi, xf, yf, dist;

void bfs() {

    while(!q.empty()) {
        int i = q.front()[0], j = q.front()[1];
        q.pop();

        for(int d = 0;d < 4;d++) {
            int ii = i + l[d], jj = j + c[d];
            if(a[ii][jj] == 0) {
                a[ii][jj] = a[i][j] +  1;
                q.push({ii, jj});
            }
        } 
    }
}

void dfs(int i, int j) {
    b[i][j] = 1;
    for(int d = 0;d < 4;d++) {
        int ii = i + l[d], jj = j + c[d];
        if(b[ii][jj] == 0 && a[ii][jj] != -1 && a[ii][jj] > dist)
            dfs(ii, jj);
    }
}

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);

    Open("barbar");

    cin >> N >> M;

    for(int i = 0;i <= N + 1;i++) 
        a[i][0] = a[i][M + 1] = -1;
    for(int i = 0;i <= M + 1;i++)
        a[0][i] = a[N + 1][i] = -1;

    for(int i = 1;i <= N;i++)
        for(int j = 1;j <= M;j++) {
            cin >> ch;
            if(ch == 'I')
                xi = i, yi = j;
            if(ch == 'O')
                xf =  i, yf = j;
            if(ch == '*')
                a[i][j] = -1;
            if(ch == 'D')
                a[i][j] = 1, q.push({i, j});
        }

    bfs();

    int l = 1, r = a[xi][yi], ans = -1;
    while(l <= r) {
        int m = (l + r) / 2;

        memset(b, 0, sizeof(b));
        dist = m;
        dfs(xi, yi);

        if(b[xf][yf] == 1) {
            ans = m;
            l = m + 1;
        } else {
            r = m - 1;
        }
    }

    cout << ans;


    return 0;
}