#include <iostream> 
using namespace std; 
 
int main() { 
    int n; 
    cin>>n; 
    int x=0; 
    for (int i=1;i<=n;i++) { 
        x+=i; 
    } 
    cout<<x<<endl; 
    return 0; 
} 
/**************************************************************
	Problem: 1002
	User: zhangailin
	Language: C++
	Result: Accepted
	Time:13 ms
	Memory:2072 kb
****************************************************************/