#include <iostream>
#include <fstream>
#include <queue>
#define fi first
#define se second
#define nmx 1005

using namespace std;
ifstream fin ("barbar.in");
ofstream fout ("barbar.out");

int n, i, j, nr, r, c, ix, iy, ox, oy, x, y, vx, vy, rez;
int v[nmx][nmx], dl[] = {-1, 0, 1, 0}, cl[] = {0, 1, 0, -1};
string s;
deque < pair< int, int>> dq;

struct Per {
    int x, y;
    bool operator < (const Per &alt) const
    {   return v[x][y] > v[alt.x][alt.y];  }
};
priority_queue < Per > pq;

int main () {
    
    fin >> r >> c;
    getline (fin, s);
    for (i = 1; i <= r; i++)    {
        getline (fin, s);
        for (j = 0; j < c; j++)    {
            if (s[j] == '.')    continue;
            if (s[j] == '*')    v[i][j + 1] = -1;
            else if (s[j] == 'D')    {
                v[i][j + 1] = 1;
                dq.push_back ({i, j+1});
            }
            else if (s[j] == 'I')    {
                ix = i;
                iy = j + 1;
            }
            else if (s[j] == 'O')    {
                ox = i;
                oy = j + 1;
            }
        }
    }
    
    while (!dq.empty()) {
        
        x = dq.front().fi;
        y = dq.front().se;
        dq.pop_front();
        
        for (j = 0; j < 4; j++) {
            vx = x + dl[j];
            vy = y + cl[j];
            if (v[vx][vy] == 0 && vx > 0 && vy > 0 && vx <= r && vy <= c) {
                v[vx][vy] = v[x][y] + 1;
                dq.push_back ({vx, vy});
            }
        }
    }
    
    bool ok = 0;
    rez = v[ix][iy];
    v[ix][iy] *= -1;
    pq.push ({ix, iy});
    while (!pq.empty()) {
        
        x = pq.top().x;
        y = pq.top().y;
        pq.pop();
        
        if (x == ox && y == oy)    {
            ok = 1;
            break;
        }
        rez = min(rez, -v[x][y]);
        
        for (j = 0; j < 4; j++) {
            vx = x + dl[j];
            vy = y + cl[j];
            if (v[vx][vy] > 1 && vx > 0 && vy > 0 && vx <= r && vy <= c) {
                
                v[vx][vy] *= -1;
                pq.push ({vx, vy});
            }
        }
    }
    
    if (ok == 0)    {
        fout << -1 << "\n";
    } else {
        fout << rez-1 << "\n";
    }
}