#include <bits/stdc++.h>

using namespace std;

const int INF = 1e9;

int r, c;
char a[1001][1001];
int mindist[1001][1001];

#define fi first
#define se second

pair <int, int> s, d;
queue <pair <int, int> > q;
pair <int, int> q1[1000001];
int st, dr;
int viz[1001][1001], cat;

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

inline bool ver(int dist)  {
    st = 1, dr = 1;
    q1[st] = s;
    cat++;
    while(st <= dr)  {
        pair <int, int> nod = q1[st];
        st++;
        int x, y;
        x = nod.fi, y = nod.se;
        for(int i = 0;i < 4;i++)  {
            int nx, ny;
            nx = x + dx[i], ny = y + dy[i];
            if(a[nx][ny] == 1 && mindist[nx][ny] >= dist && viz[nx][ny] < cat)  {
                q1[++dr] = {nx, ny};
                viz[nx][ny] = cat;
                if(nx == d.fi && ny == d.se)  {
                    return 1;
                }
            }
        }
    }
    return 0;
}

int main()  {
    freopen("barbar.in", "r", stdin);
    freopen("barbar.out", "w", stdout);
    scanf("%d%d", &r, &c);
    fgetc(stdin);
    for(int i = 1;i <= r;i++)  {
        for(int j = 1;j <= c;j++)  {
            char c;
            mindist[i][j] = INF;
            c = fgetc(stdin);
            if(c == '.')
                a[i][j] = 1;
            else if(c == 'D')
                a[i][j] = 2, q.push({i, j}), mindist[i][j] = 0;
            else if(c == 'I')
                a[i][j] = 1, s = make_pair(i, j);
            else if(c == 'O')
                a[i][j] = 1, d = make_pair(i, j);
        }
        fgetc(stdin);
    }
    while(!q.empty())  {
        pair <int, int> nod = q.front();
        q.pop();
        int x, y;x = nod.fi, y = nod.se;
        for(int i = 0;i < 4;i++)  {
            int nx, ny; nx = x + dx[i], ny = y + dy[i];
            if(a[nx][ny])  {
                if(mindist[nx][ny] > mindist[x][y] + 1)  {
                    mindist[nx][ny] = mindist[x][y] + 1;
                    q.push({nx, ny});
                }
            }
        }
    }
    int r = 0, pas = 1 << 20;
    while(pas)  {
        if(ver(r + pas))
            r += pas;
        pas >>= 1;
    }
    printf("%d", r);
    return 0;
}