#include <bits/stdc++.h>
using namespace std;

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

void constr(vector<vector<int>> &v, vector<vector<int>> &dis, queue<pair<int, int>> &q)
{
    while(!q.empty())
    {
        pair<int, int> ps = q.front();
        q.pop();
        for(int d = 0; d < 4; d++)
        {
            int nx = ps.first + dx[d];
            int ny = ps.second + dy[d];
            if(nx >= 1 && nx < v.size() && ny >= 1 && ny < v[0].size() && !v[nx][ny] && !dis[nx][ny])
            {
                dis[nx][ny] = dis[ps.first][ps.second] + 1;
                q.push({nx, ny});
            }
        }
    }
}

bool check(vector<vector<int>> &v, vector<vector<int>> &dis, int sx, int sy, int ex, int ey, int mid)
{
    queue<pair<int, int>> q;
    vector<vector<int>> vis(v.size(), vector<int>(v[0].size(), 0));
    if(dis[sx][sy] < mid) 
        return false;
    q.push({sx, sy});
    vis[sx][sy] = 1;
    while(!q.empty())
    {
        pair<int, int> ps = q.front();
        q.pop();
        if(ps.first == ex && ps.second == ey)
        {
            return true;
        }
        for(int d = 0; d < 4; d++)
        {
            int nx = ps.first + dx[d];
            int ny = ps.second + dy[d];
            if(nx >= 1 && nx < v.size() && ny >= 1 && ny < v[0].size() && !v[nx][ny] && !vis[nx][ny])
            {
                if(dis[nx][ny] >= mid)
                {
                    vis[nx][ny] = 1;
                    q.push({nx, ny});
                }
            }
        }
    }
    return false;
}

int main()
{
    freopen("barbar.in", "r", stdin);
    freopen("barbar.out", "w", stdout);
    cin.tie(nullptr)->sync_with_stdio(false);
    int n, m;
    cin >> n >> m;
    int sx, sy, ex, ey;
    queue<pair<int, int>> q;
    vector<vector<int>> v(n + 1, vector<int>(m + 1, 0));
    vector<vector<int>> dis(n + 1, vector<int>(m + 1, 0));
    for(int i = 1; i <= n; i++)
    {
        for(int j = 1; j <= m; j++)
        {
            char c;
            cin >> c;
            if(c == 'D')
            {
                q.push({i, j});
                v[i][j] = 1;
            }
            if(c == 'I')
            {
                sx = i;
                sy = j;
            }
            if(c == 'O')
            {
                ex = i;
                ey = j;
            }
            if(c == '*')
            {
                v[i][j] = 1;
            }
        }
    }
    constr(v, dis, q);
    int st = 0, dr = n * m, ans = -1;
    while(st <= dr)
    {
        int mid = (st + dr) / 2;
        if(check(v, dis, sx, sy, ex, ey, mid))
        {
            ans = mid;
            st = mid + 1;
        }
        else
        {
            dr = mid - 1;
        }
    }
    cout << ans << "\n";
}