# include <fstream>
# include <queue>
using namespace std;

ifstream f ("barbar.in");
ofstream g ("barbar.out");

const int dx[] = {1, 0, -1, 0};
const int dy[] = {0, 1, 0, -1};
int n, m;
char c;
short a[1010][1010], b[1010][1010];
queue < pair <int, int> > Q;
pair <int, int> start, finish;

void BFs ()
{
    for (; !Q.empty (); Q.pop ())
    {
        pair <int, int> ret = Q.front ();
        for (int k = 0; k < 4; ++k)
        {
            pair <int, int> acm = ret;
            acm.first += dx[k];
            acm.second += dy[k];
            if (acm.first > 0 && acm.first <= n && acm.second > 0 && acm.second <= m)
            {
                if (!a[acm.first][acm.second])
                {
                    a[acm.first][acm.second] = a[ret.first][ret.second] + 1;
                    Q.push (acm);
                }
            }
        }
    }
}

inline int ok (int X)
{
    for (int i = 1; i <= n; ++i)
        for (int j = 1; j <= m; ++j)
            b[i][j] = a[i][j];

    while (!Q.empty ()) Q.pop ();
    Q.push (start);
    for (; !Q.empty (); Q.pop ())
    {
        pair <int, int> ret = Q.front ();
        for (int k = 0; k < 4; ++k)
        {
            pair <int, int> acm = ret;
            acm.first += dx[k];
            acm.second += dy[k];
            if (acm.first > 0 && acm.first <= n && acm.second > 0 && acm.second <= m)
            {
                if (b[acm.first][acm.second] >= X && b[acm.first][acm.second] >= 0)
                {
                    b[acm.first][acm.second] = -1;
                    Q.push (acm);
                    if (acm.first == finish.first && acm.second == finish.second)
                        return 1;
                }
            }
        }
    }
    return 0;
}

inline int bs ()
{
    int i, cnt = 1 << 13;
    for (i = 1; cnt > 0; cnt >>= 1)
        if (ok (i + cnt)) i += cnt;
    return i;
}

int main ()
{
    f >> n >> m;
    for (int i = 1; i <= n; ++i)
        for (int j = 1; j <= m; ++j)
        {
            f >> c;
            if (c == 'D') Q.push (make_pair (i, j)), a[i][j] = 1;
            else
            if (c == 'I') start = make_pair (i, j);
            else
            if (c == 'O') finish = make_pair (i, j);
            else
            if (c == '*') a[i][j] = -1;
        }

    BFs ();
    int val = bs () - 1;
    g << val - (val == 0) << '\n';
    g.close ();
    return 0;
}