#include<iostream>
using namespace std;
int main(){
    int a=1,n,sum=0;
    cin>>n;
    while(a<=n){
        sum=sum+a;
        a++;
    }
    cout<<sum;
}
/**************************************************************
	Problem: 1002
	User: zouliangyin
	Language: C++
	Result: Accepted
	Time:7 ms
	Memory:2072 kb
****************************************************************/