#include<cmath>
#include<cstdio>
#include<algorithm>
#include<cstring>
#include<iostream>

using namespace std;
int main( )
{
	int N;
	cin>>N;
	if(1<=N&&N<=100)
    N=(1+N)*N/2;
    cout<<N<<endl;
		
	return 0;
}