#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ull = unsigned long long;
using Graph = vector<vector<int> >;
const int INF = 1e9;
const int MOD = 1e9+7;
const ll LINF = 1e+18;

#define REP(i, n) for (int i = 0; (i) < (int)(n); ++ (i))
#define REP2(i, s, n) for (int i = (s); i < (int)(n); i++)
#define REPB(i,n) for(int i = n-1; (int)i >= 0; --i)
#define FOREACH(x,a) for(auto& (x) : (a) 
#define YESNO(T) if(T){cout<<"YES"<<endl;}else{cout<<"NO"<<endl;}
#define yesno(T) if(T){cout<<"yes"<<endl;}else{cout<<"no"<<endl;}
#define YesNo(T) if(T){cout<<"Yes"<<endl;}else{cout<<"No"<<endl;}
#define ALL(x) x.begin(),x.end()
#define VI vector<int>
#define VL vector<ll>
#define VS vector<string>
#define VC vector<char>
#define VVI vector<vector<int> >
#define VVL vector<vector<ll> >
#define VVC vector<vector<char> >
#define VPII vector<pair<int,int> >
#define VPLL vector<pair<ll,ll> >
#define VPSI vector<pair<string,int> >

template <class T>
    inline void printVec(std::vector<T> v){
    REP(i,v.size()){
    if(i) std::cout << " ";
    std::cout << v[i];
    } std::cout << std::endl;
}

template <class T> bool chmax(T& a,T b) {
   if(a < b) {
       a = b;
       return true;
   }
   return false;
}
template <class T> bool chmin(T& a,T b) {
   if(a > b) {
       a = b;
       return true;
   }
   return false;
}
ll gcd(ll a, ll b){
   if(b == 0) return a;
   else return gcd(b , a & b);
}
ll lcm(ll a, ll b){
   return a * b / gcd(a,b);
}

int main() {
    cin.tie(0);
    ios_base::sync_with_stdio(false);

    int n;
    cin >> n;

    cout << n * (n+1) / 2 << endl;
    return 0;
}