#include<bits/stdc++.h>
using namespace std;

#define REP(i,x,y) for(ll i=x; i<=y; i++)
#define BIT(t) ((long long 1) << t)
#define PER(i,y,x) for(ll i=y; i>=x; i--)
#define SIZE(v) ll(v.size())
#define vll vector<ll>
#define vvll vector<vector<ll>>
#define pll pair<ll,ll>
#define UNIQUE(v) v.erase( unique(v.begin(), v.end()), v.end() );
typedef long long ll;
int main(){
        ll n;
        cin >> n;
        cout << n * (n + 1) / 2 << endl;
}