#include #include #include #include #include #include #include static const int MOD = 1000000007; using ll = long long; using u32 = unsigned; using namespace std; template constexpr T INF = ::numeric_limits::max() / 32 * 15 + 208; int main() { int n; cin >> n; cout << n*(n+1)/2 << "\n"; return 0; }