#include <set> #include <map> #include <list> #include <queue> #include <stack> #include <cmath> #include <ctime> #include <cstdio> #include <vector> #include <string> #include <bitset> #include <cctype> #include <cstdlib> #include <cstring> #include <utility> #include <numeric> #include <complex> #include <sstream> #include <fstream> #include <iomanip> #include <cassert> #include <iostream> #include <iterator> #include <algorithm> using namespace std; typedef long long ll; const double EPS = 1e-9; typedef vector<int> vint; typedef pair<int, int> pint; #define rep(i, n) REP(i, 0, n) #define ALL(v) v.begin(), v.end() #define MSG(a) cout << #a << " " << a << endl; #define REP(i, x, n) for(int i = x; i < n; i++) template<class T, class C> void chmax(T& a, C b){ a>b?:a=b; } template<class T, class C> void chmin(T& a, C b){ a<b?:a=b; } int main(void){ int n; cin >> n; cout << n*(n+1)/2 << endl; }