#include <bits/stdc++.h>

using namespace std;

ifstream fin("barbar.in");
ofstream fout("barbar.out");
const int di[] = {1, 0, -1, 0};
const int dj[] = {0, 1, 0, -1};
const int INF = 1e9 + 7;

struct Pozitie {
    int i, j;
} inc, sf;

char a[1002][1002];
int dist[1002][1002];
queue<Pozitie> q;
int fr[1002][1002];
int n, m, i, j;

static inline void BFS() {
    while(!q.empty()) {
        int i = q.front().i;
        int j = q.front().j;
        q.pop();

        for(int dir = 0; dir < 4; dir++) {
            int in = i + di[dir];
            int jn = j + dj[dir];

            if(!(1 <= in && in <= n && 1 <= jn && jn <= m)) continue;
            if(dist[in][jn] != 0) continue;
            if(a[in][jn] == '.' || a[in][jn] == 'D') {
                dist[in][jn] = 1 + dist[i][j];
                q.push(Pozitie{in, jn});
            }
        }
    }
}

static inline bool Verif(int d) {
    fr[inc.i][inc.j] = d;

    q.push(inc);

    while(!q.empty()) {
        int i = q.front().i;
        int j = q.front().j;
        q.pop();

        for(int dir = 0; dir < 4; dir++) {
            int in = i + di[dir];
            int jn = j + dj[dir];

            if(!(1 <= in && in <= n && 1 <= jn && jn <= m)) continue;

            if(a[in][jn] != '.') continue;

            if(fr[in][jn] == d) continue;

            if(dist[in][jn] >= d) {
                fr[in][jn] = d;
                q.push(Pozitie{in, jn});
            }
        }
    }
    return (fr[sf.i][sf.j] == d);
}

int main() {
    fin.tie(NULL);
    fout.tie(NULL);

    fin >> n >> m;
    for(i = 1; i <= n; i++) {
        for(j = 1; j <= m; j++) {
            fin >> a[i][j];
            if(a[i][j] == 'D') {
                q.push({i, j});
                dist[i][j] = 1;
            }
            else if(a[i][j] == 'I') {
                inc = Pozitie{i, j};
                a[i][j] = '.';
            }
            else if(a[i][j] == 'O') {
                sf = Pozitie{i, j};
                a[i][j] = '.';
            }
        }
    }

    BFS();

    for(i = 1; i <= n; i++) {
        for(j = 1; j <= m; j++) dist[i][j]--;
    }


    int st = 1, dr = n * m;
    int rasp = -1;

    while(st <= dr) {
        int mij = st + (dr - st) / 2;
        if(Verif(mij)) {
            rasp = mij;
            st = mij + 1;
        }
        else dr = mij - 1;
    }
    fout << rasp;

    return 0;
}