#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<math.h>
#include<iostream>
#include<algorithm>
#include<stack>
#include<queue>
#include<vector>
#include<set>
#include<map>
#include<string>
using namespace std;
typedef long long ll;
typedef pair<int,int>P;
const int INF=0x3f3f3f3f;
const double pi=acos(-1.0);
const double eps=1e-9;
int main()
{
    int n;
    scanf("%d",&n);
    printf("%d\n",n*(n+1)/2);
    return 0;
}
