#include <stdio.h>
#define DIM 1005

int A[DIM][DIM], C[2][DIM*DIM], dist[DIM][DIM], ruta[DIM][DIM], viz[DIM][DIM];
int di[] = {0, 0, -1, 1}, dj[] = {-1, 1, 0, 0};
char x;
int n, m, i, j, k, X1, X2, Y1, Y2, p, u, iv, jv, ip, jp, ok, poz, rutaC, sol;

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

int min(int a, int b) {
	return a<b?a:b;
}

int max(int a, int b) {
	return a>b?a:b;
}

void citire() {
	fscanf(f,"%d%d\n",&n,&m);
	for (i = 1; i <= n; i++) {
		for (j = 1; j <= m; j++) {

			fscanf(f,"%c",&x);
			if (x == 'I')
				X1 = i, Y1 = j, A[i][j] = -2;
			if (x == 'D')
				A[i][j] = -1;
			if (x == '*')
				A[i][j] = -2;
			if (x == 'O')
				X2 = i, Y2 = j; //A[i][j] = -2;
		}
		fscanf(f,"\n");
	}
}

void distante() {
	for (i = 1; i <= n; i++)
		for (j = 1; j <= m; j++)
			if (A[i][j] == -1)
				u++, C[0][u] = i, C[1][u] = j;

	for (p = 1; p <= u; p++) {
		ip = C[0][p], jp = C[1][p];
		for (k = 0; k <= 3; k++) {
			iv = ip + di[k];
			jv = jp + dj[k];
			if (!A[iv][jv] && iv > 0 && iv <= n && jv > 0 && jv <= m)
				if (!dist[iv][jv] || dist[ip][jp] + 1 < dist[iv][jv]) {
					u++;
					C[0][u] = iv;
					C[1][u] = jv;
					dist[iv][jv] = dist[ip][jp] + 1;
				}
		}
	}
}

void drum() {
	C[0][1] = X1, C[1][1] = Y1, ruta[X1][Y1] = DIM*DIM; //ruta[X2][Y2] = -1;
	for (p = u = 1; p <= u; p++) {
		ip = C[0][p], jp = C[1][p];
		for (k = 0; k <= 3; k++) {
			iv = ip + di[k];
			jv = jp + dj[k];
			if (!A[iv][jv] && iv > 0 && iv <= n && jv > 0 && jv <=m)
				if (!viz[iv][jv]) {
					ruta[iv][jv] = min(ruta[ip][jp], dist[iv][jv]);
					u++;
					C[0][u] = iv;
					C[1][u] = jv;
					viz[iv][jv] = u;
				}
				else
					if (min(ruta[ip][jp], dist[iv][jv]) > ruta[iv][jv]) {					
						poz = viz[iv][jv];
						rutaC = min(ruta[ip][jp], dist[iv][jv]);
						if (rutaC > ruta[ C[0][poz] ][ C[1][poz] ] )
							ruta[ C[0][poz] ][ C[1][poz] ] = rutaC;
					}
		}
	}
}

void fill(int i, int j) {
	int k;
	A[i][j] = -2;
	for (k = 0; k <= 3; k++) {
		iv = i + di[k];
		jv = j + dj[k];
		if (A[iv][jv] != -2 && iv > 0 && iv <= n && jv > 0 && jv <=m) {
			if (iv == X2 && jv == Y2) {
				ok = 1;
				return ;
			}
			fill(iv, jv);
		}
	}
}

void verif() {
	ok = 0;
	fill(X1, Y1);
}

int main() {
	
	citire();
	
	distante();
	
	drum();
	
	verif();
	
	if (ok) {	
		sol = min(max(max(ruta[X2-1][Y2], ruta[X2+1][Y2]), max(ruta[X2][Y2-1], ruta[X2][Y2+1])), ruta[X2][Y2]);
		fprintf(g,"%d",sol);
	}
	else
		fprintf(g,"-1");
	
	fclose(f);
	fclose(g);
	
	return 0;
}