#include<bits/stdc++.h> 
using namespace std;
int main(){
    int s,n;
    cin>>s;
    n=(1+s)*s/2;
    cout<<n; 
    return 0;
}
/**************************************************************
	Problem: 1002
	User: jiangyuanfeng
	Language: C
	Result: Compile Error
****************************************************************/