#include<iostream>
#include<fstream>
using namespace std;


ifstream fin("cifra.in");
ofstream fout("cifra.out");

int  main() {
    int n,c,k=0,i;
    fin>>n;
    for(i=1;i<=n;i++)
    k=k+i*i;



    fout<<k%10;

    fin.close();
    fout.close();

    return 0;

}