#include<bits/stdc++.h>
using namespace std;
int main(){
    int a=1,c=0,b;
    cin>>b;
    while(a<=b){
        c=a+c;  
        a++;   
    }
    cout<<c;
}
/**************************************************************
	Problem: 1002
	User: zhangyilei
	Language: C++
	Result: Accepted
	Time:14 ms
	Memory:2072 kb
****************************************************************/