#include <iostream>
#include <fstream>
#include <cstring>
#include <vector>
#include <algorithm>
#include <bitset>
#include <cmath>
#include <queue>
#define pii pair <int, int>

using namespace std;

const int oo = 2e9;

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

int n, m, d[1005][1005];

char a[1005][1005];
queue <pii> q;
bitset <1005> viz[1005];

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


void read() {
    fin >> n >> m;
    for (int i = 1; i <= n; i++) {
            for(int j=1; j <= m; j++)
                fin >> a[i][j];
    }
    fin.close();
}


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


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

void Fill(int i, int j, int val) {
    viz[i][j] = 1;
    for (int k = 0; k < 4; k++)
    {
        int x = i + dx[k];
        int y = j + dy[k];
        if (a[x][y] != '*' && viz[x][y] == 0 && d[x][y] >= val)
            Fill (x, y, val);
    }
}

int BinSearch()
{
    int left, right, mid, maxval = -1;
    left = 0;
    right = min(d[start.first][start.second], d[finish.first][finish.second]);
    while (left <= right)
    {
        int mid = (left + right) / 2;
        Fill(start.first, start.second, mid);
        if (viz[finish.first][finish.second] == 1)
        {
            maxval = mid;
            left = mid + 1;
        }
        else right = mid - 1;
        for (int i = 1; i <= n; i++)
            viz[i].reset();
    }
    return maxval;
}

void solve() {
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= m; j++) {
            if (a[i][j] == 'D') {
                q.push({ i, j });
                d[i][j] = 0;
            }
            else if (a[i][j] == 'I') start = { i, j };
            else if (a[i][j] == 'O') finish = { i, j };
        }
    Lee();
    fout << BinSearch() << "\n";
}


int main() {
    read();
    Board();
    solve();
    return 0;
}