#include <bits/stdc++.h>

using namespace std;

long sumOfGroup(long k) {
    // Return the sum of the elements of the k'th group.
        long i=((k*(k-1))/2);
        long m = ((k*(k+1))/2);
        long sum = (m*m) - (i*i);
        
        return sum;
}

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