#include<bits/stdc++.h>
using namespace std;
int main(){
	int n;
	scanf("%d",&n);
	printf("%d",(1+n)*n/2);
	return 0;
}
/**************************************************************
	Problem: 1002
	User: chenxurui
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/