#include<bits/stdc++.h>
using namespace std;


int main()
{
	//freopen("in.txt","r",stdin);
//	freopen("out.txt","w",stdout);
	long long int a,b,c,n,r,i,j,k,ans;
	while(cin>>n>>r)
	{
        ans=1;
        a=n-r;
        for(i=n;i>a;i--)
        {
        	ans*=i;
        	while(ans%10==0)
        	{
        		ans/=10;
        	}
          ans%=1000000000;
        }
        cout<<ans%10<<endl;
	}
	return 0;
}