#include<stdio.h>
#include<iostream>
#include<algorithm>
#include<cmath>
#include<map>
#include<vector>
#include<string.h>
#include<set>
#define inf 0x3f3f3f3f
using namespace std;
int main()
{
    int n;
    cin>>n;
    int sum=0;
    for(int i=1;i<=n;i++)
        sum+=i;
    printf("%d\n",sum);
}
