#define _GLIBCXX_DEBUG
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
template<typename T>bool chmax(T &a,const T &b){if(a<b){a=b;return true;}else{return false;}}
template<typename T>bool chmin(T &a,const T &b){if(a>b){a=b;return true;}else{return false;}}
/* ASCII
[0:48],[1:49],[2:50],[3:51],[4:52],[5:53],[6:54],[7:55],[8:56],[9:57],
[A:65],[B:66],[C:67],[D:68],[E:69],[F:70],[G:71],[H:72],[I:73],[J:74],[K:75],[L:76],[M:77],
[N:78],[O:79],[P:80],[Q:81],[R:82],[S:83],[T:84],[U:85],[V:86],[W:87],[X:88],[Y:89],[Z:90],
[a:97],[b:98],[c:99],[d:100],[e:101],[f:102],[g:103],[h:104],[i:105],[j:106],[k:107],[l:108],[m:109],
[n:110],[o:111],[p:112],[q:113],[r:114],[s:115],[t:116],[u:117],[v:118],[w:119],[x:120],[y:121],[z:122]
*/


int main(void){
    int N; cin >> N;
    int ans = 0;
    for(int i = 1; i <= N; i++){
        ans += i;
    }
    cout << ans << endl;
}