#include<bits/stdc++.h>

using namespace std;

typedef long long LL;

struct cww{cww(){
    ios::sync_with_stdio(false);cin.tie(0);
    cout<<fixed;
    cout<<setprecision(10);
}}star;
#define fin "\n"
#define FOR(i,bg,ed) for(int i=(bg);i<(ed);i++)
#define REP(i,n) FOR(i,0,n)

#define fi first
#define se second
#define pb push_back

template <typename T>inline void chmin(T &l,T r){l=min(l,r);}
template <typename T>inline void chmax(T &l,T r){l=max(l,r);}

template <typename T>
istream& operator>>(istream &is,vector<T> &v){
    for(auto &it:v)is>>it;
    return is;
}

int main(){
    int N;
    cin>>N;
    cout<< N*(N+1)/2<<endl;
    return 0;
}