#include<stdio.h>
struct cd{
	int i,j,cost;
};
const int di[5]={0,0,1,-1,0};
const int dj[5]={0,1,0,0,-1};

long m[1001][1001];

int main()
{
	freopen("barbar.in","r",stdin);
	freopen("barbar.out","w",stdout);
	int r,c,i,j,k=1,x1,x2,y1,y2,in=1,sf=2,iv,jv,max=0,p,poz;
	char ch;
	cd q[1001],a;
	scanf("%d%d\n",&r,&c);
	for(i=1;i<=r;i++){
		for(j=1;j<=c;j++){
			scanf("%c",&ch);
			if(ch=='.'){
				m[i][j]=99999;
			}
			if(ch=='D'){
				m[i][j]=0;
			    q[k].i=i;
			    q[k].j=j;
			    q[k].cost=0;
			    k++;
			}
			if(ch=='I'){
				x1=i;
				y1=j;
				m[i][j]=99999;
			}
			if(ch=='O'){
				x2=i;
				y2=j;
				m[i][j]=99999;
			}
			if(ch=='*'){
				m[i][j]=-1;
			}
		}
		scanf("\n");
	}
	sf=k;
	
	
	while(in<sf)
	{
		a=q[in];
		in++;
		for(i=1;i<=4;i++)
		{
			iv=a.i+di[i];
			jv=a.j+dj[i];
			if((1<=iv)&&(iv<=r)&&(1<=jv)&&(jv<=c)&&(m[iv][jv]!=-1)&&(a.cost+1<m[iv][jv]))
			{
				m[iv][jv]=a.cost+1;
				q[sf].i=iv;
				q[sf].j=jv;
				q[sf].cost=a.cost+1;
			    sf++;
			    if(q[sf].cost>max){
					max=q[sf].cost;
				}
			}
		}
	}
	for(p=1;p*2<=max;p*=2);
	for(poz=0;p;p/=2){
		if(poz+p<=max){
			poz+=p;
		    while(in<sf)
			{
				a=q[in];
				in++;
				for(i=1;i<=4;i++)
				{
					iv=a.i+di[i];
					jv=a.j+dj[i];
					if((1<=iv)&&(iv<=r)&&(1<=jv)&&(jv<=c)&&(m[iv][jv]!=-1)&&(a.cost+1<m[iv][jv]))
					{
						m[iv][jv]=a.cost+1;
						q[sf].i=iv;
						q[sf].j=jv;
						q[sf].cost=a.cost+1;
			    		sf++;
			    		if(q[sf].cost>max)
						{
						max=q[sf].cost;
						}
					}
				}
			}
	return 0;
}