//ALEXANDRU MICLEA

#include <vector>
#include <algorithm>
#include <string>
#include <cstring>
#include <queue>
#include <map>
#include <set>
#include <unordered_map>
#include <time.h>
#include <iomanip>
#include <deque>
#include <math.h>
#include <cmath>
#include <assert.h>
#include <stack>
#include <bitset>
#include <random>
#include <chrono>
#include <iostream>
#include <array>

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<double, double> pdd;
typedef vector<ll> vll;
typedef vector<int> vi;
typedef vector<vector<int> > vvi;
typedef vector<vector<ll> > vvll;
typedef vector<vector<pll> > vvpll;
typedef vector<pll> vpll;
typedef vector<pii> vpii;
const ll MOD = 1e9 + 7;
double eps = 1e-6;
#define forn(i,e) for(ll i = 1; i <= e; i++)
#define for0n(i,e) for(ll i = 0; i < (e); i++)
#define forsn(i,s,e) for(ll i = s; i <= e; i++)
#define rforn(i,s) for(ll i = s; i >= 1; i--)
#define rfor0n(i,s) for(ll i = s; i >= 0; i--)
#define rforsn(i,s,e) for(ll i = s; i >= e; i--)
#define ln "\n"
#define dbg(x) cout<<#x<<" = "<<x<<ln
#define mp make_pair
#define pb push_back
#define fi first
#define se second
#define llinf 2e18
#define iinf 1e9
#define all(x) (x).begin(), (x).end()
#define sz(x) ((ll)(x).size())

//VARIABLES

int t[1005][1005];
int p[1005][1005];
int drag[1005][1005];

queue<pair<int, int>> q, qdrag;
int dx[] = { 1,0,-1,0 };
int dy[] = { 0,1,0,-1 };

pair <int, int> I, O;

int m, n;

//FUNCTIONS

void lee_drag() {

    while (!qdrag.empty()) {
        pair <int, int> now = qdrag.front();
        qdrag.pop();

        for (int i = 0; i <= 3; i++) {
            int x = now.first + dx[i];
            int y = now.second + dy[i];

            if (x < 1 || y < 1 || x > n || y > m) continue;
            if (p[x][y]) continue;
            if (drag[x][y] <= drag[now.first][now.second] + 1) continue;


            drag[x][y] = drag[now.first][now.second] + 1;
            qdrag.push({ x,y });
        }
    }
}

int lee(int val) {
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= m; j++) {
            t[i][j] = 1e9;
        }
    }
    q.push(I);
    t[I.first][I.second] = 1;


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

        for (int i = 0; i <= 3; i++) {
            int x = now.first + dx[i];
            int y = now.second + dy[i];

            if (x < 1 || y < 1 || x > n || y > m) continue;
            if (p[x][y]) continue;
            if (t[x][y] <= t[now.first][now.second] + 1) continue;
            if (drag[x][y] < val) continue;


            t[x][y] = t[now.first][now.second] + 1;
            q.push({ x,y });
        }
    }

    return t[O.first][O.second] != 1e9;
}

int cautbin(int left, int right) {
    int ans = -1;


    while (left <= right) {
        int mid = (left + right);
        mid >>= 1;

        if (lee(mid)) {
            //incearca mai la dreapta
            ans = mid;
            left = mid + 1;
        }
        else {
            right = mid - 1;
        }
    }

    return ans;
}


//MAIN
int main() {

#ifdef INFOARENA
    freopen("barbar.in", "r", stdin);
    freopen("barbar.out", "w", stdout);
#endif


    cin >> n >> m;

    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= m; j++) {
            t[i][j] = 1e9;
            drag[i][j] = 1e9;
            char c; cin >> c;
            if (c == 'I') I = { i, j };
            if (c == 'O') O = { i, j };
            if (c == 'D') {
                qdrag.push({ i, j });
                drag[i][j] = 0;
            }
            if (c == '*') p[i][j] = 1;
        }

    }

    lee_drag();
    /*for (int i = 1; i <= n; i++) {
        for (int j = 0; j < m; j++) {
            cout << drag[i][j] % int(1e9) << ' ';
        }
        cout << '\n';
    }
    */
    int ans = cautbin(1, n * m);

    cout << ans;

    return 0;
}