#include <cstdio>
#include <vector>
#include <queue>
#include <cstring>
using namespace std;
const int NMAX = 1000;
const int MMAX = 1000;
const int INF = 2.e9;
int di[]= {-1 , 0 , 1 , 0};
int dj[]= {0 , 1 , 0 , -1};
struct dragoni
{
    int x , y;
};
dragoni temp1 , temp2;
int drg[NMAX + 5][MMAX + 5] , d[NMAX + 5][MMAX + 5] , n , m , xs , ys , xf , yf;
bool a[NMAX + 5][MMAX + 5];
char s[MMAX + 5];
int valid(int x , int y)
{
    if(x >= 1 && x <= n && y >= 1 && y <= m && a[x][y] == 0)
        return 1;
    return 0;
}
void init()
{
    int i;
    for(i = 1 ; i <= n ; i ++)
        memset(d[i] , 0 , sizeof(d[i]));
}
int verif(int k)
{
    int i;
    init();
    queue <dragoni> q;
    d[xs][ys] = drg[xs][ys];
    temp1.x = xs;
    temp1.y = ys;
    q.push(temp1);
    while(!q.empty())
    {
        temp1 = q.front();
        q.pop();
        for(i = 0 ; i < 4 ; i ++)
        {
            temp2.x = temp1.x + di[i];
            temp2.y = temp1.y + dj[i];
            if(valid(temp2.x , temp2.y) && drg[temp2.x][temp2.y] != 0 && drg[temp2.x][temp2.y] >= k && d[temp2.x][temp2.y] == 0)
            {
                d[temp2.x][temp2.y] = 1;
                q.push(temp2);
            }
        }
    }
    return d[xf][yf];
}
int bs()
{
    int st , dr , med , last;
    st = 1;
    dr = drg[xs][ys];
    last = -1;
    while(st <= dr)
    {
        med = (st + dr) / 2;
        if(verif(med))
        {
            last = med;
            st = med + 1;
        }
        else
            dr = med - 1;
    }
    return last;
}
int main()
{
    freopen("barbar.in" , "r" , stdin);
    freopen("barbar.out" , "w" , stdout);
    int i , j;
    scanf("%d%d\n" , &n , &m);
    queue <dragoni> q;
    for(i = 1 ; i <= n ; i ++)
    {
        scanf("%s\n" , s);
        for(j = 0 ; j < m ; j ++)
        {
            drg[i][j + 1] = INF;
            if(s[j] == '*')
                a[i][j + 1] = 1;
            else if(s[j] == 'I')
            {
                xs = i;
                ys = j + 1;
            }
            else if(s[j] == 'O')
            {
                xf = i;
                yf = j + 1;
            }
            else if(s[j] == 'D')
            {
                temp1.x = i;
                temp1.y = j + 1;
                q.push(temp1);
                drg[i][j + 1] = 0;
            }
        }
    }
    while(!q.empty())
    {
        temp1 = q.front();
        q.pop();
        for(i = 0 ; i < 4 ; i ++)
        {
            temp2.x = temp1.x + di[i];
            temp2.y = temp1.y + dj[i];
            if(valid(temp2.x , temp2.y) && drg[temp2.x][temp2.y] > drg[temp1.x][temp1.y] + 1)
            {
                drg[temp2.x][temp2.y] = drg[temp1.x][temp1.y] + 1;
                q.push(temp2);
            }
        }
    }
    printf("%d\n" , bs());
    return 0;
}