#include <fstream>
#define N 1005

using namespace std;
			ifstream q("barbar.in");
			ofstream w("barbar.out");
int b[1005][1005],m,n,p,x2,y2,x1,y1;
char c[1005][1005];

struct ab{
		int x,y;
		};
ab v[1005*1005];

const int lin[]={0,0,1,-1},col[]={1,-1,0,0};

void lee(int x,int y){
	
for(int t=0;t<4;t++)

  if(b[x+lin[t]][y+col[t]] == -2){
  		b[x+lin[t]][y+col[t]] = b[x][y]+1;
	    v[++v[0].x].x = x+lin[t];
   		v[v[0].x].y = y+col[t];
  }
}
   
   
void lee2(int x,int y){
	for(int t=0;t<4;t++)
  		if(c[x+lin[t]][y+col[t]] == -1 && b[x+lin[t]][y+col[t]] >= p){
					   				v[++v[0].x].x = x+lin[t];
									v[v[0].x].y = y+col[t];
									c[x+lin[t]][y+col[t]] = 1;
		}
}


void curat()
{
	int i,j;
	
	for(i=1;i<=m;i++)
	  for(j=1;j<=n;j++) c[i][j] = -1;
}
    
    
int solve(int lung){
	int i;
		
	v[0].x = 1;
	p = lung;
	
	v[1].x = x1;
	v[1].y = y1;
	
	curat();
	
	if(b[x1][y1]<p)
	 return 0;
	for(i=1;i<=v[0].x;i++){
					if(c[x2][y2] == 1)
	   				return 1;
	 				lee2(v[i].x,v[i].y);
	}
	if(c[x2][y2] == 1)
	 return 1;
return 0;
}



int main(){
	
int i,j,st=0,dr=N*N*10,mij;
char x;
		q>>m>>n;
		
		for(i=1;i<=m;i++)
		  for(j=1;j<=n;j++){
		    				q>>x;
							if(x == 'D'){
								 v[++v[0].x].x = i;
								 v[v[0].x].y = j;
							}
							else
			 				if(x == '*') b[i][j] = -1;
			 				else b[i][j] = -2;
			 				
							 if(x == 'O'){
							  	x2 = i;
							    y2 = j;
							 }
							 if(x == 'I'){
							  x1 = i;
							  y1 = j;
						  	 }
		  }	
       
	   for(i=1;i<=v[0].x;i++)
  			lee(v[i].x,v[i].y);
  			
		while(st <= dr){
   					 mij = (st+dr)/2;
					 if(solve(mij)) st = mij+1;
						else
						 dr = mij-1;
		}
		w<<st-1;
return 0;
}