#include #define rep(i, x) for(ll i = 0; i < x; i++) #define rep2(i, x) for(ll i = 1; i <= x; i++) #define all(a) (a).begin(),(a).end() using ll = long long; using ld = long double; const ll INF = 10000000000000000; using namespace std; signed main() { ll n; cin >> n; cout << (n + 1) * n /2 << endl; return 0; }