#include using namespace std; #define all(x) x.begin(),x.end() #define rep(i, n) for (int i = 0; i < (int)(n); i++) template inline bool chmax(T&a,T b){if(a inline bool chmin(T&a,T b){if(a>b){a=b;return 1;}return 0;} using ll = long long; int n; int main() { cin >> n; cout << n*(1+n)/2 << endl; }