#include <iostream>
#include <fstream>
#include <bitset>
#include <queue>
#include <set>
#include <bitset>
using namespace std;

#define MAXN 1005
#define INF 0x3f3f3f3f

class heap{
private:
    pair<int, pair<int, int> > a[MAXN];
    int sz = 0;
    # define father(x) (x >> 1)
    # define left_son(x) (x << 1)
    # define right_son(x) ((x << 1) + 1)
public:
    heap() {};

    void insert(pair<int, pair<int, int> > x) {
        a[sz] = x;
        int k = sz;
        sz++;

        while ((k > 0) && (a[k] < a[father(k)])) {
            swap(a[k], a[father(k)]);
            k = father(k);
        }
    }

    pair<int, pair<int, int> > top() {
        if (sz > 0) {
            return a[0];
        }
        return make_pair(0, make_pair(0, 0));
    }

    void pop() {
        sz--;
        a[0] = a[sz];
        int k = 0;
        while (right_son(k) < sz && (a[k] > a[left_son(k)] || a[k] > a[right_son(k)])) {
            if (a[left_son(k)] > a[right_son(k)]) {
                swap(a[k], a[right_son(k)]);
                k = right_son(k);
            } else {
                swap(a[k] , a[left_son(k)]);
                k = left_son(k);
            }
        }
        if (left_son(k) < sz && a[k] > a[left_son(k)]) {
            swap(a[k] , a[left_son(k)]);
        }
    }

    bool empty() {
        if (sz == 0) {
            return true;
        }
        return false;
    }

    int size() {
        return sz;
    }
};

FILE *f = fopen("barbar.in", "r");
FILE *g = fopen("barbar.out", "w");

int n, m, startx, starty, stopx, stopy, sol;
int a[MAXN][MAXN];
queue< pair<int, int> > q;
int d[4][2] = {{0, -1}, {-1, 0}, {0, 1}, {1, 0}};
heap mst;
bitset<MAXN> viz[MAXN];

bool isvalid(int i, int j) {
    if (1 <= i && i <= n && 1 <= j && j <= m && a[i][j] != -1) {
        return true;
    }
    return false;
}

void lee1()
{
    while (!q.empty()) {
        int x = q.front().first;
        int y = q.front().second;
        q.pop();

        for (int i = 0; i < 4; i++) {
            int nx = x + d[i][0];
            int ny = y + d[i][1];

            if (isvalid(nx, ny) && a[nx][ny] > a[x][y] + 1) {
                a[nx][ny] = a[x][y] + 1;
                q.push(make_pair(nx, ny));
            }
        }
    }
}

void lee2()
{
    mst.insert(make_pair(-a[startx][starty], make_pair(startx, starty)));
    sol = a[startx][starty];
    while (!mst.empty()) {
        int x = mst.top().second.first;
        int y = mst.top().second.second;
        mst.pop();

        if (x == stopx && y == stopy) {
            sol = min(sol, a[x][y]);
            break;
        }

        if (viz[x][y] == true) {
            continue;
        }
        viz[x][y] = true;

        sol = min(sol, a[x][y]);

        for (int i = 0; i < 4; i++) {
            int nx = x + d[i][0];
            int ny = y + d[i][1];

            if (isvalid(nx, ny)) {
                mst.insert(make_pair(-a[nx][ny], make_pair(nx, ny)));
            }
        }
    }
}

int main()
{
    fscanf(f, "%d %d\n", &n, &m);
    char buf[MAXN];
    for (int i = 1; i <= n; i++) {
        fgets(buf + 1, sizeof(buf), f);
        for (int j = 1; j <= m; j++) {
            switch (buf[j]) {
                case '.':
                    a[i][j] = INF;
                    break;
                case 'D':
                    q.push(make_pair(i, j));
                    break;
                case 'I':
                    startx = i;
                    starty = j;
                    a[i][j] = INF;
                    break;
                case 'O':
                    stopx = i;
                    stopy = j;
                    a[i][j] = INF;
                    break;
                case '*':
                    a[i][j] = -1;
                    break;
            }
        }
    }

    lee1();
    lee2();

    fprintf(g, "%d\n", sol);

    fclose(f);
    fclose(g);
    return 0;
}