#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;
typedef vector<ll> v;
typedef string str;
typedef double dou;
#define FOR(i,a,b) for(ll i=a;i<b;i++)
#define f0r(i,b) FOR(i,0,b)
#define SORT(a) sort(a.begin(),a.end());
#define llin(a,n) f0r(i,n) {cin>>a[i];}
#define vin(a,n) f0r(i,n) {ll tmp;cin>>tmp;a.push_back(tmp);}
#define douketa(n) cout<<fixed<<setprecision(n);
str ALP="ABCDEFGHIJKLMNOPQRSTUVWXYZ";
str alp="abcdefghijklmnopqrstuvwxyz";
dou pi=3.141592653589793;
int main(){
    ll n;
    cin>>n;
    cout<<n*(n+1)/2;
}