#include<cstdio>
#include<fstream>
#include<iostream>
#include<iomanip>
#include<algorithm>
#include<vector>
#include<bitset>
#include<deque>
#include<queue>
#include<set>
#include<map>
#include<cmath>
#include<cstring>
#include<ctime>
#include<cstdlib>
#include<unordered_map>

#define ll long long
#define pb push_back
#define mp make_pair
#define pii pair<int,int>
#define pll pair<ll,ll>

using namespace std;

const int nmax = 1005;
const int inf = (1LL << 31) - 1;

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

int n, m, i, j, sx, sy, fx, fy, x, y, newx, newy, l, r, mi, sol;
int d[nmax][nmax];
bool can[nmax][nmax];
char a[nmax][nmax];

deque<pii> q;

bool check(int mini)
{
    if(d[sx][sy] < mini) return 0;

    memset(can, 0, sizeof(can));
    can[sx][sy] = 1;
    q.pb(mp(sx, sy));
    while(!q.empty())
    {
        x = q.front().first;
        y = q.front().second;
        q.pop_front();

        for(int i = 0; i < 4; i++)
        {
            newx = x + dx[i];
            newy = y + dy[i];
            if(!can[newx][newy] && d[newx][newy] >= mini)
            {
                can[newx][newy] = 1;
                q.pb(mp(newx, newy));
            }
        }
    }

    return can[fx][fy];
}

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

    scanf("%d%d", &n, &m);

    for(i = 1; i <= n; i++)
        scanf("%s", a[i] + 1);

    for(i = 1; i <= n; i++)
        for(j = 1; j <= m; j++)
            d[i][j] = inf;

    for(i = 1; i <= n; i++)
        for(j = 1; j <= m; j++)
        {
            if(a[i][j] == 'D')
            {
                q.pb(mp(i, j));
                d[i][j] = 0;
            }
            else if(a[i][j] == 'I')
            {
                sx = i;
                sy = j;
            }
            else if(a[i][j] == 'O')
            {
                fx = i;
                fy = j;
            }
        }

    while(!q.empty())
    {
        x = q.front().first;
        y = q.front().second;
        q.pop_front();

        for(i = 0; i < 4; i++)
        {
            newx = x + dx[i];
            newy = y + dy[i];
            if(d[newx][newy] == inf && a[newx][newy] != '*')
            {
                d[newx][newy] = d[x][y] + 1;
                q.pb(mp(newx, newy));
            }
        }
    }

    for(i = 0; i <= n + 1; i++)
        for(j = 0; j <= m + 1; j++)
            if(d[i][j] == inf || i == 0 || i == n + 1 || j == 0 || j == m + 1)
                d[i][j] = -1;

    l = 0;
    r = min(n, m);
    while(l <= r)
    {
        mi = (l + r) / 2;
        if(check(mi))
        {
            sol = mi;
            l = mi + 1;
        }
        else r = mi - 1;
    }

    printf("%d\n",sol);

    return 0;
}