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

int main()
{int T,i,S,N,c;
    fstream f("cifra.in",ios::in);
    f>>T;
    N=1;
    S=0;
    for(i=1;i<=T;i++)
      {S=S+(N*N);
      N=N+1;}
c=S%10;
 fstream g("cifra.out",ios::out);
 g<<c;
 f.close();g.close();
    return 0;
}