#include<stdio.h>
#include<string>
using namespace std;
FILE*f=fopen("barbar.in","r");
FILE*g=fopen("barbar.out","w");

int di[4] = {-1,1,0,0};
int dj[4] = {0,0,-1,1};
int i,j,iinit,jinit,ifinal,jfinal,A[1024][1024],nrc,C[2][1024 * 1024];
int N,M,p,u,d,ic,jc,iv,jv,m;
char x,viz[1024][1024];

inline void precalculare() {
	
	p = 1; u = nrc;
	while ( p <= u ){
		ic = C[0][p]; jc = C[1][p];
		
		for ( d = 0 ; d < 4 ; ++d ){
			iv = ic + di[d]; jv = jc + dj[d];
			if ( iv >= 1 && iv <= N && jv >= 1 && jv <= M && A[iv][jv] == -1 ){
				++u;
				C[0][u] = iv;
				C[1][u] = jv;
				A[iv][jv] = A[ic][jc] + 1;
			}
			
		}
		++p;
	}
}

int coada(int dist) {
	int p = 1;
	int u = 1;
	C[0][1] = iinit; C[1][1] = jinit;
	memset(viz,0,sizeof(viz)); int ho = 0;
	if ( A[iinit][jinit] < dist )
		return ho;
	
	while ( p <= u && (!ho) ) {
		ic = C[0][p]; jc = C[1][p];
		
		for ( d = 0 ; d < 4 ; ++d ){
			iv = ic + di[d]; jv = jc + dj[d];
			
			if ( iv >= 1 && iv <= N && jv >= 1 && jv <= M && ( ! viz[iv][jv] ) && A[iv][jv] >= dist ){
				++u;
				C[0][u] = iv;
				C[1][u] = jv;
				viz[iv][jv] = 1;
				if ( iv == ifinal && jv == jfinal ){
					ho = 1;
					break;
				}
			}
			
		}
		++p;
	}
	return ho;
	
}

int main () {
	
	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' ) iinit = i, jinit = j,A[i][j] = -1;
			else	if ( x == 'D' )	{C[0][++nrc] = i; C[1][nrc] = j;}
			else	if ( x == '*' ) A[i][j] = -2;
			else	if ( x == '.' ) A[i][j] = -1;
			else	if ( x == 'O' ) A[i][j] = -1, ifinal = i,jfinal = j;
		}
		fscanf(f,"\n");
	}
	
	precalculare();
	
	p = 0 ; u = N * M;
	
	while ( p <= u ) {
		
		m = p + ( u - p ) / 2;
		
		// daca da este 1 se poate traversa la o distanta mai mare sau egala decat m
		
		if ( coada( m ) )
			p = m + 1;
		else
			u = m - 1;
		
	}
	if ( u < 0 )	fprintf(g,"-1\n");
	else
		fprintf(g,"%d\n",u);
	
	fclose(f);
	fclose(g);
	return 0;
}