#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(ll i=0;i<(ll)n;i++)
#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()
#define mod 998244353
#define dai 5000000000000000000LL
#define sho -dai
#define eps 1e-14
#define fi(x) cout<<fixed<<setprecision(x);
using ll=long long;
using un=unsigned long long;
using ld=long double;
using st=string;
using ch=char;
using bo=bool;
using P=pair<ll,ll>;
using T=tuple<ll,ll,ll>;
using vi=vector<ll>;
using vs=vector<st>;
using vc=vector<ch>;
using vb=vector<bo>;
using vp=vector<P>;
using sp=set<P>;
using ss=set<st>;
using si=set<ll>;
using vvi=vector<vi>;
using vvs=vector<vs>;
using vvb=vector<vb>;
using vvc=vector<vc>;
using vvp=vector<vp>;
using vsi=vector<set<ll>>;
const ll dx[4]={0,1,0,-1};
const ll dy[4]={1,0,-1,0};
const ll INF = 1e18;
int main() {
	un n;
	cin>>n;
	cout<<(un)n*(n+1)/2<<endl;
}