#include <bits/stdc++.h>

using namespace std;

long long K = 1e6;

int main() {
    long long k;
    cin >> k;

    
    
    long long l = k*(k+1)/2;
    long long f = k*(k-1)/2;
    
    long long sum=(1+1+2*(l-1))/2*l;
    long long sum1 = (1+1+2*(f-1))/2*f;;    
    
    
    cout << sum-sum1 << endl;
    return 0;
}