#include <algorithm>
#include <climits>
#include <fstream>
#include <queue>
#include <string>
#include <tuple>
#include <vector>

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

int n, m;
char a[1005][1005];
int d[1005][1005], maxDistance[1005][1005];
int dx[] = {-1, 0, 0, 1};
int dy[] = {0, -1, 1, 0};
std::queue<std::pair<int, int>> q;

bool inside(int i, int j) {
    return !(i < 1 || i > n || j < 1 || j > m);
}

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

void solve(int xs, int ys) {
    std::priority_queue<std::tuple<int, int, int>> pq;
    maxDistance[xs][ys] = d[xs][ys];
    pq.push(std::make_tuple(maxDistance[xs][ys], xs, ys));

    while (!pq.empty()) {
        auto [val, x, y] = pq.top();
        pq.pop();
        if (val < maxDistance[x][y]) {
            continue;
        }
        for (int k = 0; k < 4; k++) {
            int i{x + dx[k]}, j{y + dy[k]};
            if (inside(i, j) && a[i][j] != '*') {
                int newDistance{std::min(d[i][j], val)};
                if (newDistance > maxDistance[i][j]) {
                    maxDistance[i][j] = newDistance;
                    pq.push(std::make_tuple(newDistance, i, j));
                }
            }
        }
    }
}

int main() {
    int xs = 0, ys = 0, x = 0, y = 0;

    if (!(fin >> n >> m)) {
        fout << -1 << "\n";
        return 0;
    }

    for (int i = 1; i <= n; i++) {
        std::string s;
        fin >> s;
        for (int j = 1; j <= m && j <= (int)s.size(); j++) {
            a[i][j] = s[j - 1];
        }
    }

    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= m; j++) {
            d[i][j] = INT_MAX;
            maxDistance[i][j] = -1;
        }
    }

    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= m; j++) {
            if (a[i][j] == 'D') {
                d[i][j] = 0;
                q.push(std::make_pair(i, j));
            } else if (a[i][j] == 'I') {
                xs = i;
                ys = j;
            } else if (a[i][j] == 'O') {
                x = i;
                y = j;
            }
        }
    }

    calculateDistances();
    solve(xs, ys);

    fout << maxDistance[x][y] << "\n";
    fout.close();
    return 0;
}