#include<stdio.h>
#include<queue>
#include<string.h>
#include<algorithm>
using namespace std;
struct MyStruct {int x,y;} f,start;
inline MyStruct make(int x,int y) {MyStruct a; a.x=x;a.y=y; return a;}
int n,m,a[1005][1005],d[1005][1005];
int viz[1005][1005];
queue<MyStruct> q;
int dx[]={0,1,0,-1};
int dy[]={-1,0,1,0};
bool ok(int p)
{
	if(d[start.x][start.y]==-2) return 1;
	if(d[start.x][start.y]<p) return 0;
	q.push(start);
	memset(viz,0,sizeof(viz));
	viz[start.x][start.y]=1;
	while(!q.empty())
	{
		MyStruct temp=q.front();
		for(int i=0;i<4;i++)
		{
			temp.x+=dx[i];
			temp.y+=dy[i];
			if(d[temp.x][temp.y]>=p && viz[temp.x][temp.y]==0)
			{
				viz[temp.x][temp.y]=1;
				q.push(temp);
			}
			temp.x-=dx[i];
			temp.y-=dy[i];
		}
		q.pop();
	}
	return viz[f.x][f.y];
}
int main()
{
	freopen("barbar.in","r",stdin);
	freopen("barbar.out","w",stdout);
	int n,m,i,j;char ch;
	scanf("%d %d\n",&n,&m);
	for(i=1;i<=n;i++)
		for(j=1;j<=m;j++)
			d[i][j]=-2;
	for(i=0;i<=n+1;i++)
		d[i][0]=d[i][m+1]=-1;
	for(i=0;i<=m+1;i++)
		d[0][i]=d[n+1][i]=-1;
	for(i=1;i<=n;i++,scanf("%c",&ch))
		for(j=1;j<=m;j++)
		{
			scanf("%c",&ch);
			if(ch=='*') d[i][j]=-1;
			else
				if(ch=='.');
				else
					if(ch=='D') {d[i][j]=0;q.push(make(i,j));}
					else
						if(ch=='O') {f.x=i;f.y=j;}
						else {start.x=i;start.y=j;}
		}
	//calculare matrice d1
	MyStruct temp;
	while(!q.empty())
	{
		temp=q.front();
		for(i=0;i<4;i++)
		{
			temp.x+=dx[i];
			temp.y+=dy[i];
			if(d[temp.x][temp.y]==-2)
			{
				d[temp.x][temp.y]=d[q.front().x][q.front().y]+1;
				q.push(temp);
			}
			temp.x-=dx[i];
			temp.y-=dy[i];
		}
		q.pop();
	}
	int st,dr,med,last;
	st=0;dr=n*m;last=-1;
	while(st<=dr)
	{
		med=(st+dr)/2;
		if(ok(med))
		{
			last=med;
			st=med+1;
		}
		else
			dr=med-1;
	}
	printf("%d\n",last);
	return 0;
}