#include <bits/stdc++.h>

using namespace std;

#define USE_STD_IO 0
#if USE_STD_IO
    #define fin cin
    #define fout cout
#else
    ifstream fin("barbar.in");
    ofstream fout("barbar.out");
#endif // USE_STD_IO

const int DI[] = {1, -1, 0, 0};
const int DJ[] = {0, 0, 1, -1};
struct Pozitie {
    int i, j;
};
queue<Pozitie> q;

int n, m, i, j, dist[1002][1002];
char mat[1002][1002];
Pozitie start, dest;

bool viz[1002][1002];

static inline void DistDragoni() {
    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(0 == dist[in][jn] && '*' != mat[in][jn]) {
                dist[in][jn] = 1 + dist[i][j];
                q.push(Pozitie{in, jn});
            }
        }
    }
}

static inline bool Parcurg(int mi) {
    memset(viz, false, sizeof(viz));

    q.push(start);
    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(!viz[in][jn] && mi <= dist[in][jn] && '*' != mat[in][jn]) {
                viz[in][jn] = true;
                q.push(Pozitie{in, jn});
            }
        }
    }
    return viz[dest.i][dest.j];
}

static inline int CautBin() {
    int st = 1, dr = n * m;
    int rasp = -1;
    while(st <= dr) {
        int mij = st + (dr - st) / 2;
        if(Parcurg(mij)) {
            rasp = mij;
            st = mij + 1;
        }
        else dr = mij - 1;
    }
    return rasp;
}

int main() {
    if(USE_STD_IO) ios_base::sync_with_stdio(false);
    fin.tie(NULL);
    fout.tie(NULL);

    fin >> n >> m;
    for(i = 1; i <= n; i++) {
        for(j = 1; j <= m; j++) {
            fin >> mat[i][j];
            switch(mat[i][j]) {
                case 'I': start = {i, j}; break;
                case 'D': q.push(Pozitie{i, j}); break;
                case 'O': dest = {i, j}; break;
            }
        }
    }
    DistDragoni();
    fout << CautBin();

    return 0;
}