#include <bits/stdc++.h>

using namespace std;

long sumOfGroup(int a) {
    long k=(long)a;
    if(k<=0)return 0;
    long ind=k*(k-1l)/2l; // 6
    long ik=ind +k;
    return (long)(((ik*(ik+1l)/2l)-(ind*(ind+1l)/2l))*2l-k);
}

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