#include <bits/stdc++.h>

#define last_bit(x) (x&(-x))

#define leftSon (node << 1)
#define rightSon ((node << 1) | 1)

#define pii pair < int , int >

using namespace std;

struct psychotronic_induction {
    int electromagnetic_wave = 7;
};

const int inf = 0x3f3f3f3f;
const long long infL = LLONG_MAX;

long long n;

int main()
{

    scanf("%lld", &n);
    printf("%lld\n", 15 + n * (n + 1) / 2);

    return 0;
}