#include <bits/stdc++.h>
using namespace std;
const int NMAX = 1000;
const int PERETE = '*';
const int DRAGON = 'D';
const int GOL = '.';

int n, m, camera, istart, jstart, ifinal, jfinal;
char a[NMAX + 2][NMAX + 2];
int dist[NMAX + 2][NMAX + 2];
bool folosit[NMAX + 2][NMAX + 2];
int dx[] = {1, -1, 0, 0};
int dy[] = {0, 0, -1, 1};

bool inmat(int i, int j)
{
    return i >= 0 && i < n && j >= 0 && j < m;
}
void bfs_dragoni()
{
    int i, j, inou, jnou;
    queue<pair<int, int>> q;
    for (i = 0; i < n; i++)
    {
        for (j = 0; j < m; j++)
        {
            if (a[i][j] == DRAGON)
            {
                q.push({i, j});
                dist[i][j] = 1;
            }
        }
    }
    while (!q.empty())
    {
        i = q.front().first;
        j = q.front().second;
        q.pop();
        for (int d = 0; d < 4; d++)
        {
            inou = i + dx[d];
            jnou = j + dy[d];
            if (inmat(inou, jnou) && dist[inou][jnou] == 0 && a[inou][jnou] != PERETE)
            {
                dist[inou][jnou] = dist[i][j] + 1;
                q.push({inou, jnou});
            }
        }
    }
}

bool bfs(int dmin)
{
    memset(folosit, false, sizeof(folosit));
    int i, j, inou, jnou;
    queue<pair<int, int>> q;
    q.push({istart, jstart});
    while (!q.empty())
    {
        i = q.front().first;
        j = q.front().second;
        q.pop();
        for (int d = 0; d < 4; d++)
        {
            inou = i + dx[d];
            jnou = j + dy[d];
            if (dist[inou][jnou] >= dmin && !folosit[inou][jnou])
            {
                folosit[inou][jnou] = true;
                q.push({inou, jnou});
            }
        }
    }
    if (folosit[ifinal][jfinal])
    {
        return true;
    }
    return false;
}
int main()
{
    freopen("barbar.in", "r", stdin);
    freopen("barbar.out", "w", stdout);

    scanf("%d %d", &n, &m);
    for (int i = 0; i < n; i++)
    {
        char linie[NMAX];
        scanf("%s", linie);
        for (int j = 0; j < m; j++)
        {
            a[i][j] = linie[j];
            if (linie[j] == 'I')
            {
                istart = i;
                jstart = j;
            }
            else if (linie[j] == 'O')
            {
                ifinal = i;
                jfinal = j;
            }
        }
    }

    bfs_dragoni();

    /*for (int i = 0; i < n; i++)
    {
        for (int j = 0; j < m; j++)
        {
            if (a[i][j] == PERETE)
            {
                printf("* ");
            }
            else if (a[i][j] == 'I')
            {
                printf("I ");
            }
            else if (a[i][j] == 'O')
            {
                printf("O ");
            }
            else if (a[i][j] == 'D')
            {
                printf("D ");
            }
            else
                printf("%d ", dist[i][j] - 1);
        }
        printf("\n");
    }*/

    int st, dr, m;
    st = 1;
    dr = 1000;
    while (st <= dr)
    {
        m = (st + dr) / 2;
        if (bfs(m))
        {
            st = m + 1;
        }
        else
        {
            dr = m - 1;
        }
    }
    printf("%d", dr - 1);
    return 0;
}