#include<bits/stdc++.h>
using namespace std;
int main(){
    int n,i,s=0;
    cin>>n;
    i=1;
    while(i<=n){
        s=s+i;
        i=i+1;
    }
    cout<<s;
}
/**************************************************************
	Problem: 1002
	User: wenda
	Language: C++
	Result: Accepted
	Time:9 ms
	Memory:2072 kb
****************************************************************/