#include <bits/stdc++.h>

using namespace std;

int n, m;
pair<int, int> b, e;

queue< pair<int, int> > q;
int mp[1005][1005];
bool a[1005][1005];

const int sj[] = {0, -1, 0, 1};
const int sd[] = {-1, 0, 1, 0};

void lee(void)
{
    int i;
    pair<int, int> tp, auxp;
    while(!q.empty())
    {
        tp = q.front();
        q.pop();
        for(i = 0; i < 4; ++i)
        {
            auxp.first = tp.first + sj[i];
            auxp.second = tp.second + sd[i];
            if(mp[auxp.first][auxp.second] == 0)
            {
                mp[auxp.first][auxp.second] = mp[tp.first][tp.second] + 1;
                q.push(auxp);
            }
        }
    }
}

void clear_table()
{
    int i, j;
    for(i = 1; i <= n; ++i)
        for(j = 1; j <= m; ++j)
            a[i][j] = true;
}

bool tryfill(int i, int j, int& val)
{
    if(mp[i][j] > val && a[i][j])
    {
        a[i][j] = false;
        return ((i == e.first && j == e.second) ||
                tryfill(i, j-1, val) || tryfill(i, j+1, val) ||
                tryfill(i-1, j, val) || tryfill(i+1, j, val));
    }
    return false;
}

int bsrc(int& n, int& m)
{
    int stanga = 1, dreapta = n+m+2, med;
    while(stanga <= dreapta)
    {
        clear_table();
        med = (stanga + dreapta) / 2;
        if(tryfill(b.first, b.second, med))
            stanga = med + 1;
        else
            dreapta = med - 1;
    }
    return (stanga+dreapta) / 2;
}

int main()
{
    char c;
    int i, j;

    ifstream fin("barbar.in");
    ofstream fout("barbar.out");

    fin >> n >> m;

    for(i = 1; i <= n; ++i)
    {
        fin.get();
        for(j = 1; j <= m; ++j)
        {
            fin.get(c);
            if(c == 'I')
            {
                b.first = i;
                b.second = j;
            }
            else if(c == 'O')
            {
                e.first = i;
                e.second = j;
            }
            else if(c == 'D')
            {
                mp[i][j] = 1;
                q.push(make_pair(i, j));
            }
            else if(c == '*')
            {
                mp[i][j] = -1;
            }
        }
    }

    for(i = 0; i <= n+1; ++i)
        mp[i][0] = mp[i][m+1] = -1;
    for(i = 0; i <= m+1; ++i)
        mp[0][i] = mp[n+1][i] = -1;
    

    lee();
    fout << bsrc(n, m);
}