#include<iostream>
#include<vector>
#include<string>
using namespace std;

#define FOR(k,m,n) for(int (k)=(m);(k)<(n);(k)++)
#define rep(i,n) FOR((i),0,(n))

typedef long long ll;

const int INF=1e9+7;

int main(){
	int n;
	cin>>n;
	cout<<n*(n+1)/2<<endl;
}