#include <cstdio>
#include <cstring>
#include <queue>
#include <utility>
using namespace std;

#define Nmax 1002
#define inf 0x3f3f3f3f
#define mp make_pair
#define x first
#define y second

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

queue < pair < int , int > > Q;
pair < int , int > start, finish ,aux;

int N, M, cost[Nmax][Nmax];
const int d[4][2] = { {-1,0}, {0,1}, {1,0}, {0,-1} };

bool inside ( int x, int y ){
	if ( x > 0 && y > 0 && x <= N && y <= M )
		return 1;
	return 0;
}

void BFS (){
	
	while ( !Q.empty() ){
		aux = Q.front ();
		Q.pop();
		
		for ( int i = 0; i < 4; ++i ){
			int xx = aux.x + d[i][0];
			int yy = aux.y + d[i][1];
			
			if ( inside ( xx, yy ) && cost[xx][yy] > cost[aux.x][aux.y] + 1 ){
				Q.push ( mp ( xx, yy ) );
				cost[xx][yy] = cost[aux.x][aux.y] + 1; 
			}
		}
	}
}

bool viz[Nmax][Nmax];

bool isRoad ( int k ){
	Q.push ( start );
	
	memset ( viz, 0, sizeof ( viz ) );
	
	while ( !Q.empty() ){
		aux = Q.front ();
		Q.pop();
		
		for ( int i = 0; i < 4; ++i ){
			int xx = aux.x + d[i][0];
			int yy = aux.y + d[i][1];
			
			if ( !viz[xx][yy] && inside ( xx, yy ) && cost[xx][yy] >= k ){
				Q.push ( mp ( xx, yy ) );
				viz[xx][yy] = 1;
			}
		}
	}
	
	return viz[finish.x][finish.y];
}

int main (){
	char c;
	
	fscanf ( f, "%d%d%*c", &N, &M );
	
	for ( int i = 1; i <= N; ++i ){
		for ( int j = 1; j <= M; ++j ){
			fscanf ( f, "%c", &c );
			switch ( c ){
				case '.':
					cost[i][j] = inf;
					break;
				
				case '*':
					cost[i][j] = -1;
					break;
				
				case 'D':
					cost[i][j] = 0;
					Q.push ( mp ( i, j ) );
					break;
				
				case 'I':
					start.x = i;
					start.y = j;
					break;
				
				case 'O':
					cost[i][j] = inf;
					finish.x = i;
					finish.y = j;
					break;
			}
		}
		fscanf ( f, "%*c" );
	}
	
	BFS ();
	
	int st = 1, dr = max ( cost[start.x][start.y], cost[finish.x][finish.y] );
	int mid, sol;
	bool exist = 0;
	
	while ( st <= dr ){
		mid = ( st + dr ) >> 1;
		
		if ( isRoad ( mid ) ){
			sol = mid;
			exist = 1;
			st = mid + 1;
		}
		else
			dr = mid - 1;
	}
	
	if ( !exist )
		fprintf ( g, "-1" );
	else
		fprintf ( g, "%d", sol );
	
	return 0;
}