#include <bits/stdc++.h>
using namespace std;

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

char a[1004][1004];
int d[1004][1004], v[1004][1004], n, m;
int xs, ys, xf, yf;
queue <pair <int, int> > q;
int dx[] = {-1, 1, 0, 0};
int dy[] = {0, 0, -1, 1};

void Citire ()
{
    int i, j;
    fin >> n >> m;
    for (i = 1; i <= n; i++)
        for (j = 1; j <= m; j++)
        {
            fin >> a[i][j];
            d[i][j] = 2e9;
            if (a[i][j] == 'D')
            {
                q.push({i, j});
                d[i][j] = 0;
            }
            else if (a[i][j] == 'I')
                xs = i, ys = j;
            else if (a[i][j] == 'O')
                xf = i, yf = j;
        }
    fin.close();
}

void Border ()
{
    int i;
    for (i = 0; i <= n + 1; i++)
        a[i][0] = a[i][m+1] = '*';
    for (i = 1; i <= m; i++)
        a[0][i] = a[n+1][i] = '*';
}

void Lee ()
{
    int i, j, x, y, k;
    while (!q.empty())
    {
        x = q.front().first;
        y = q.front().second;
        q.pop();
        for (k = 0; k < 4; k++)
        {
            i = x + dx[k];
            j = y + dy[k];
            if (a[i][j] != '*' && d[i][j] > d[x][y] + 1)
            {
                q.push({i, j});
                d[i][j] = d[x][y] + 1;
            }
        }
    }
}

void Filll (int D)
{
    int i, j, x, y, k;
    q.push({xf, yf});
    v[xf][yf] = 1;
    while (!q.empty())
    {
        x = q.front().first;
        y = q.front().second;
        q.pop();
        for (k = 0; k < 4; k++)
        {
            i = x + dx[k];
            j = y + dy[k];
            if (a[i][j] != '*' && d[i][j] >= D && v[i][j] == 0)
            {
                v[i][j] = 1;
                q.push({i, j});
            }
        }
    }
}

void Rez()
{
    int i, j, low, high, mid, D;
    low = 1; high = 1e6;
    D = -1;
    while (low <= high)
    {
        mid = (low + high) / 2;
        for (i = 1; i <= n; i++)
            for (j = 1; j <= m; j++)
                v[i][j] = 0;
        Filll (mid);
        if (!v[xs][ys])
            high = mid - 1;
        else
        {
            D = mid;
            low = mid + 1;
        }
    }
    fout << D << "\n";
}

int main()
{
    Citire();
    Lee();
    Rez();
    fout.close();
    return 0;
}