#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: panjinyan
	Language: C++
	Result: Accepted
	Time:15 ms
	Memory:2072 kb
****************************************************************/