#include <iostream>
#include <fstream>
#include <queue>

using namespace std;

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

struct cel {
    int x, y;
};

const short NMAX = 1000;
const short dx[] = {-1, 0, 1, 0};
const short dy[] = {0, 1, 0, -1};
char a[NMAX+5][NMAX+5];
short d[NMAX+5][NMAX+5];
short n, m;
cel in, out;
queue<cel> q;

void clear()
{
    while (!q.empty()) q.pop();
}

bool valid(cel z)
{
    return z.x >= 1 && z.x <= n && z.y >= 1 && z.y <= n;
}

bool ok(short val)
{
    if (d[in.x][in.y] < val) return false;

    q.push({in.x, in.y});

    while (!q.empty()) {
        cel z = q.front();
        q.pop();

        if (z.x == out.x && z.y == out.y) {
            clear();
            return true;
        }

        for (short dir = 0; dir < 4; dir++) {
            cel t = {z.x+dx[dir], z.y+dy[dir]};

            if (valid(t) && d[t.x][t.y] >= val && d[t.x][t.y] != -1) q.push({t.x, t.y});
        }
    }

    return false;
}

int main()
{
    fin>>n>>m;

    for (short i = 1; i <= n; i++)
        for (short j = 1; j <= m; j++) {
            fin>>a[i][j], d[i][j] = -2;

            if (a[i][j] == 'D') d[i][j] = 0, q.push({i, j});
            if (a[i][j] == '*') d[i][j] = -1;
            if (a[i][j] == 'I') in = {i, j};
            if (a[i][j] == 'O') out = {i, j};
        }

    while (!q.empty()) {
        cel z = q.front();
        q.pop();

        for (short dir = 0; dir < 4; dir++) {
            cel t = {z.x+dx[dir], z.y+dy[dir]};

            if (valid(t) && d[t.x][t.y] == -2) q.push({t.x, t.y}), d[t.x][t.y] = d[z.x][z.y]+1;
        }
    }

    short l = 0, r = n+m, sol = -1;

    while (l <= r) {
        short mid = (l+r)/2;

        if (ok(mid)) sol = mid, l = mid+1;
        else r = mid-1;
    }

    fout<<sol;
    return 0;
}