#include<bits/stdc++.h>
using namespace std;
int main(){
	int n,s;
    cin>>n;
	s=(n+1)*(n/2);
	cout<<s<<endl;
    return 0;
}
/**************************************************************
	Problem: 1002
	User: xiaojingxuan
	Language: C++
	Result: Accepted
	Time:9 ms
	Memory:2072 kb
****************************************************************/