#include<bits/stdc++.h>
using namespace std;
int main(){
    int n,m=0;
    cin>>n;
    for(int i=1;i<=n;i=i+1){
        m=m+i;
    }
    cout<<m;
}

/**************************************************************
	Problem: 1003
	User: zhengzihao
	Language: C++
	Result: Wrong Answer
****************************************************************/