#include <fstream>
#include <string>
#include <queue>
#pragma optimize GCC ("Ofast")
#define int long long

using namespace std;

ifstream cin ("barbar.in");
ofstream cout ("barbar.out");

using your_mom = pair <int, int>;

const int N = 1030;
int a[N + 1][N + 1], d[N + 1][N + 1], b[N + 1][N + 1];

int dx[] = {-1, 0, 1, 0};
int dy[] = {0, 1, 0, -1};

queue <your_mom> q, qd;

string s;

int n, m, ci, cf, li, lf;

bool inside (int x, int y)
{
    return (x >= 1 && x <= n && y >= 1 && y <= m);
}

bool oklee (int val)
{
    for (int i = 1; i <= n; ++i)
        for (int j = 1; j <= m; ++j)
            a[i][j] = b[i][j];
    if (d[li][ci] <= val)
        return 0;
    q.push({li, ci});
    a[li][ci] = 1;
    while (!q.empty())
    {
        int x = q.front().first;
        int y = q.front().second;
        q.pop();
        for (int i = 0; i < 4; ++i)
        {
            int xx = x + dx[i];
            int yy = y + dy[i];
            if (inside (xx, yy) && !a[xx][yy] && d[xx][yy] > val)
                a[xx][yy] = a[x][y] + 1, q.push({xx, yy});
        }

    }
    if (a[lf][cf])
        return 1;
    return 0;

}

int cb (int st, int dr)
{
    int med, last = -1;
    while (st <= dr)
    {
        int med = (st + dr) >> 1;
        if (oklee (med))
        {
            st = med + 1;
            last = med;
        }
        else
            dr = med - 1;
    }
    return last;
}

void precalc ()
{
    while (!qd.empty())
    {
        int x = qd.front().first;
        int y = qd.front().second;
        qd.pop();
        for (int i = 0; i < 4; ++i)
        {
            int xx = x + dx[i];
            int yy = y + dy[i];
            if (inside (xx, yy) && !d[xx][yy])
                d[xx][yy] = d[x][y] + 1, qd.push({xx, yy});
        }
    }
}

signed main()
{
    cin >> n >> m;
    for (int i = 1; i <= n; ++i)
    {
        cin >> s;
        for (int j = 0; j < s.size(); ++j)
        {
            if (s[j] == 'I')
                ci = j + 1, li = i;
            if (s[j] == 'O')
                cf = j + 1, lf = i;
            if (s[j] == 'D')
                qd.push({i, j + 1}), d[i][j + 1] = 1, a[i][j + 1] = b[i][j + 1] = -1;

            if (s[j] == '*')
                a[i][j + 1] = b[i][j + 1] = -1;

        }
    }
    precalc();
    int valcb = cb (1, N * N);
    cout << valcb << '\n';
    return 0;
}