UVa 10212

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

typedef long long int      ll;

int main()
{
    ll n, m;
    while(cin>>n>>m){
        if(m==0){
            cout<<1<<'\n';
            continue;
        }
        ll ans =1,x=n-m;
        for(int i=n;i>x;i--){
            ans*=i;
            while(ans%10==0){
                ans/=10;
            }
            ans%=10000000000;
        }
        cout<<ans%10<<'\n';
    }
    return 0;
}