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

ll sumOfGroup(ll k) {
    // Return the sum of the elements of the k'th group.
    ll num1=(k*(k-1))/2,num2=(k*(k+1))/2;
    ll sum1=(num1*(2+(num1-1)*2))/2;
    ll sum2=(num2*(2+(num2-1)*2))/2;
    return sum2-sum1;
}

int main() {
    ll k;
    cin >> k;
    ll answer = sumOfGroup(k);
    cout << answer << endl;
    return 0;
}