#include <bits/stdc++.h>
using namespace std;
ifstream f("barbar.in");
ofstream g("barbar.out");
const int N = 1024;
int n, m, xs, ys, xf, yf, answer = 0, viz[N][N], d[N][N], valid(int, int);
int dx[] = {0, 0, -1, 1};
int dy[] = {1, -1, 0, 0};
char c;
void Search(int, int, int);
queue <pair<int, int>> q;
int main()
{
    f >> n >> m;
    for(int i = 1; i <= n; i++)
        for(int j = 1; j <= m; j++)
        {
            f >> c;
            if(c == 'I')
                xs = i, ys = j;
            else if(c == 'O')
                xf = i, yf = j;
            else if(c == '*')
                d[i][j] = -1;
            else if(c == 'D')
                d[i][j] = 1, q.push({i, j});
        }
    while(!q.empty())
    {
        int x, y;
        tie(x, y) = q.front();
        q.pop();
        for(int i = 0; i < 4; i++)
        {
            int new_x = x + dx[i], new_y = y + dy[i];
            if(valid(new_x, new_y) && (d[new_x][new_y] == 0 || d[new_x][new_y] > d[x][y] + 1))
            {
                d[new_x][new_y] = d[x][y] + 1;
                q.push({new_x, new_y});
            }
        }
    }
    Search(xs, ys, d[xs][ys]);
    g << answer - 1;
    return 0;
}
int valid(int x, int y)
{
    if(x < 1 || x > n || y < 1 || y > m || d[x][y] == -1)
        return 0;
    return 1;
}
void Search(int x, int y, int actualmax)
{
    if(x == xf && y == yf)
    {
        answer = max(answer, actualmax);
        return;
    }
    viz[x][y] = 1;
    vector<tuple<int, int, int>> v;
    for(int i = 0; i < 4; i++)
    {
        int new_x = x + dx[i], new_y = y + dy[i];
        if(valid(new_x, new_y) && !viz[new_x][new_y] )
            v.push_back(make_tuple(d[new_x][new_y], new_x, new_y));
    }
    sort(v.begin(), v.end());
    for(int i = v.size() - 1; i >= 0; i--)
    {
        int new_x, new_y, dist;
        tie(dist, new_x, new_y) = v[i];
        Search(new_x, new_y, min(dist, actualmax));
    }
}