#include <bits/stdc++.h>

using namespace std;

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

const int MAXN = 1100;

int N, M, dist[MAXN][MAXN], xs, ys, xf, yf;
bool viz[MAXN][MAXN];
char v[MAXN][MAXN];

int dx[4] = {-1, 0, 0, 1};
int dy[4] = {0, -1, 1, 0};

bool isOkay(int minDist)
{
    queue< pair<int, int> > coada;
    memset(viz, 0, sizeof(viz));
    coada.push(make_pair(xs, ys));

    if (dist[xs][ys] < minDist) return 0;

    while (!coada.empty())
    {
        pair<int, int> a = coada.front();
        coada.pop();
        if (a.first == xf && a.second == yf)
            return 1;
        for (int i = 0 ; i < 4; ++i)
        {
            int nx = a.first + dx[i];
            int ny = a.second + dy[i];
            if (nx > 0 && nx <= N && ny > 0 && ny <= M && dist[nx][ny] >= minDist && !viz[nx][ny] && v[nx][ny] != '*')
            {
                viz[nx][ny] = 1;
                coada.push(make_pair(nx, ny));
            }
        }
    }
    return 0;

}


int cauta_binar()
{
    int last = 0, st = 0, dr = N + M;

    while (st <= dr)
    {
        int mid = (st + dr) / 2;
        if (isOkay(mid))
        {
            last = mid;
            st = mid + 1;
        }
        else
            dr = mid - 1;
    }

    return last;
}

int main()
{
    fin >> N >> M;
    fin.get();

    for (int i = 1; i <= N; ++i)
        fin.getline(v[i] + 1, MAXN);

    queue< pair<int, int> > coada;

    for (int i = 1; i <= N; ++i)
        for (int j = 1; j <= M; ++j)
        {
            if (v[i][j] == 'D')
            {
                coada.push(make_pair(i, j));
                dist[i][j] = 1;
            }
            if (v[i][j] == 'I')
            {
                xs = i;
                ys = j;
            }
            if (v[i][j] == 'O')
            {
                xf = i;
                yf = j;
            }
        }


    while (!coada.empty())
    {
        pair<int, int> a = coada.front();
        coada.pop();

        for (int i = 0 ; i < 4; ++i)
        {
            int nx = a.first + dx[i];
            int ny = a.second + dy[i];
            if (nx > 0 && nx <= N && ny > 0 && ny <= M && !dist[nx][ny] && v[nx][ny] != '*')
            {
                dist[nx][ny] = dist[a.first][a.second] + 1;
                coada.push(make_pair(nx, ny));
            }
        }
    }

    fout << cauta_binar() - 1;

    return 0;
}