#include <fstream>
#include <queue>
#include <climits>

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) {
    if (i < 1 || i > n || j < 1 || j > m) {
        return false;
    }
    return true;
}

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() {
    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] != '*') {
                int newDistance{std::min(d[i][j], maxDistance[x][y])};
                if (newDistance > maxDistance[i][j]) {
                    maxDistance[i][j] = newDistance;
                    q.push(std::make_pair(i, j));
                }
            }
        }
    }
}

int main() {
    int xs, ys, x, y;
    fin >> n >> m;
    fin.ignore();
    for (int i = 1; i <= n; i++) {
        fin.getline((a[i] + 1), 1000);
    }

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

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

    maxDistance[xs][ys] = d[xs][ys];
    q.push(std::make_pair(xs, ys));
    solve();

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