#include using namespace std; typedef long long ll; typedef long double ld; #define rep(i, a, b) for(ll i = (ll)a; i < (ll)b; i++) #define irep(i, v) for(auto i = (v).begin(); i != (v).end(); i++) #define ALL(v) (v).begin(), (v).end() #define SZ(v) (ll)(v).size() const ll INF = 1e18; const ld EPS = 1e-10; int main(){ cin.tie(0); ios::sync_with_stdio(false); srand((unsigned)time(NULL)); cout << fixed << setprecision(20); ll n; cin >> n; cout << n * (n + 1) / 2 << endl; return 0; }