#include <bits/stdc++.h>

using namespace std;

long long sumOfGroup(long long k) {
    // Return the sum of the elements of the k'th group.
    long long first = k*(k-1)/2;
    long long last = first + k - 1;
    long long sumToK = (first==0? 0: first*(first-1)/2);
    long long sumToLast = last*(last+1)/2;
    return 2*(sumToLast - sumToK) + k;
}

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