/**
  *  Worg
  */
#include <queue>
#include <cstdio>
#include <utility>
#include <cstring>

#define fi          first
#define se          second
#define mp          make_pair
#define MAX_R       1 + 1000

using namespace std;
FILE *fin=freopen("barbar.in","r",stdin);
FILE *fout=freopen("barbar.out","w",stdout);

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

queue < pair<int,int> > Q;

bool viz[MAX_R][MAX_R];
char a[MAX_R][MAX_R];
int dmin[MAX_R][MAX_R], sol[MAX_R][MAX_R];

int r, c, x1, y1, x2, y2;

void readData() {

    scanf("%d %d ", &r, &c);
    for(int i = 1; i <= r; ++i)
        gets(a[i] + 1);
}

void setMinDist() {


    for(int i = 1; i <= r; ++i)
        for(int j = 1; j <= c; ++j) {

            if(a[i][j] == 'D') {

                viz[i][j] = 1;
                Q.push(mp(i, j));
            }
            else if(a[i][j] == '*') {

                dmin[i][j] = -1;
                viz[i][j] = 1;
            }
            else if(a[i][j] == 'I') {

                x1 = i, y1 = j;
            }

            else if(a[i][j] == 'O') {

                x2 = i, y2 = j;
            }
        }

    int x, y, X, Y;
    while(!Q.empty()) {

        x = Q.front().fi, y = Q.front().se;
        Q.pop();

        for(int i = 0; i < 4; ++i) {

            X = x + dx[i];
            Y = y + dy[i];
            if(X && Y && X <= r && Y <= c && !viz[X][Y]) {

                dmin[X][Y] = dmin[x][y] + 1;
                Q.push(mp(X, Y));
                viz[X][Y] = 1;
            }
        }
    }
}

bool check(int dist) {

    if(dmin[x1][y1] < dist)
        return 0;

    memset(viz, 0, sizeof(viz));
    viz[x1][y1] = 1;
    Q.push(mp(x1, y1));

    int x, y, X, Y;
    while(!Q.empty()) {

        x = Q.front().fi, y = Q.front().se;
        Q.pop();

        if(x == x2 && y == y2) {

            while(!Q.empty())
                Q.pop();
            return 1;
        }

        for(int i = 0; i < 4; ++i) {

            X = x + dx[i];
            Y = y + dy[i];
            if(X && Y && X <= r && Y <= c && !viz[X][Y] && dmin[X][Y] >= dist) {

                Q.push(mp(X, Y));
                viz[X][Y] = 1;
            }
        }
    }
    return 0;
}

int main() {

    readData();
    setMinDist();
    int low = 0, high = r + c, mid, sol = 0;


    while(low <= high) {

        mid = (high + low) >> 1;
        if(check(mid))
            sol = mid, low = mid + 1;
        else
            high = mid - 1;
    }
    printf("%d", sol);
    return 0;
}