#include <fstream>
using namespace std;

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

int n, m, stx, sty, sfx, sfy;
int dx[4] = {-1, 0, 1, 0};
int dy[4] = {0, 1, 0, -1};
int  a[1002][1002], b[1002][1002];

struct Element {
    int ab, ord;
}aux, work, v[1000000];

int modul(int a) {
    if (a >= 0)
        return a;
    return -a;
}

int distanta(int x1, int y1, int x2, int y2) {
    return modul((x1-x2)) + modul((y1-y2));
}

void read() {
    char c;
    fin >> n >> m;
    for (int i=1; i<=n; i++) {
        for (int j=1; j<=m; j++) {
            fin >> c;
            if (c == 'I') {
                a[i][j] = -1;
                stx = i;
                sty = j;
            }
            if (c == 'O') {
                a[i][j] = -2;
                sfx = i;
                sfy = j;
            }
            if (c == 'D')
                a[i][j] = -3;
            if (c == '*') {
                a[i][j] = -4;
            }
        }
    }
    for (int i=0; i<=n+1; i++)
      a[i][0] = a[i][m+1] = -4;
    for (int j=0; j<=m+1; j++)
      a[0][j] = a[n+1][j] = -4;
}

void dragons() {
    for (int i=1; i<=n; i++)
        for (int j=1; j<=m; j++) {
            if (a[i][j] == -3) {
                for (int aux1=1; aux1<=n; aux1++)
                    for (int aux2=1; aux2<=m; aux2++) {
                        if (a[aux1][aux2] > 0)
                            a[aux1][aux2] = min(distanta(i, j, aux1, aux2), a[aux1][aux2]);
                        else
                            if (a[aux1][aux2] == 0)
                                a[aux1][aux2] = distanta(i, j, aux1, aux2);
                    }
            }
        }
}

void copying() {
    for (int i=1; i<=n; i++)
        for (int j=1; j<=m; j++)
            b[i][j] = a[i][j];
    for (int i=0; i<=n+1; i++)
      b[i][0] = b[i][m+1] = -4;
    for (int j=0; j<=m+1; j++)
      b[0][j] = b[n+1][j] = -4;
}

int drum(int k) {
    copying();
    int inc=0, sf=0;
    aux.ab = stx;
    aux.ord = sty;
    v[0] = aux;
    while (inc <= sf) {
        aux = v[inc++];
        for (int i=0; i<4; i++) {
            work.ab = aux.ab + dx[i];
            work.ord = aux.ord + dy[i];
            if (b[work.ab][work.ord] >= k) {
                v[++sf] = work;
            }
	    if ( b[work.ab][work.ord] == -2 )
		return 1;
        }
        b[aux.ab][aux.ord] = -4;
    }
    return 0;
}

int caut (int s, int d) {
    int r;
    if (s > d)
        return -1;
    else
        {
            r =(s+d)/2;
            if (drum(r) == 1 && drum(r+1) == 0)
                return r;
            if (drum(m) == 0)
                return caut(s,r-1);
            else
                return caut(r+1,d);
        }
}

int main() {
    int big;
    read();
    big = 2 * max(n, m) - 2;
    dragons();
    fout << caut(1, big);
    return 0;
}