#include "bits/stdc++.h"
#define MOD 1000000007
#define INF 11234567890
#define in std::cin
#define out std::cout
#define rep(i,N) for(LL i=0;i<N;++i)
typedef long long int LL;

int N;

int main()
{
	in >> N;
	out << N*(N + 1) / 2 << std::endl;
	return 0;
}