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

const int NMAX = 1005;
const int PERETE = '*';
const int DRAGON = 'D';

int n, m, istart, jstart, ifinal, jfinal;
char a[NMAX][NMAX];
int dist[NMAX][NMAX];
bool folosit[NMAX][NMAX];
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()
{
    queue<pair<int, int>> q;
    memset(dist, -1, sizeof(dist)); // -1 = nedeterminat

    for (int i = 0; i < n; i++)
        for (int j = 0; j < m; j++)
            if (a[i][j] == DRAGON)
            {
                q.push({i, j});
                dist[i][j] = 0;
            }

    while (!q.empty())
    {
        int i = q.front().first;
        int j = q.front().second;
        q.pop();
        for (int d = 0; d < 4; d++)
        {
            int inou = i + dx[d];
            int jnou = j + dy[d];
            if (inmat(inou, jnou) && dist[inou][jnou] == -1 && a[inou][jnou] != PERETE)
            {
                dist[inou][jnou] = dist[i][j] + 1;
                q.push({inou, jnou});
            }
        }
    }
}

bool bfs(int dmin)
{
    memset(folosit, false, sizeof(folosit));

    if (dist[istart][jstart] < dmin)
        return false;

    queue<pair<int, int>> q;
    q.push({istart, jstart});
    folosit[istart][jstart] = true;

    while (!q.empty())
    {
        int i = q.front().first;
        int j = q.front().second;
        q.pop();

        for (int d = 0; d < 4; d++)
        {
            int inou = i + dx[d];
            int jnou = j + dy[d];
            if (inmat(inou, jnou) && !folosit[inou][jnou] && a[inou][jnou] != PERETE && dist[inou][jnou] >= dmin)
            {
                folosit[inou][jnou] = true;
                q.push({inou, jnou});
            }
        }
    }

    return folosit[ifinal][jfinal];
}

int main()
{
    freopen("barbar.in", "r", stdin);
    freopen("barbar.out", "w", stdout);

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

    bfs_dragoni();

    int st = 0, dr = n * m, rezultat = -1;
    while (st <= dr)
    {
        int mij = (st + dr) / 2;
        if (bfs(mij))
        {
            rezultat = mij;
            st = mij + 1;
        }
        else
        {
            dr = mij - 1;
        }
    }

    printf("%d\n", rezultat);
    return 0;
}