#include<bits/stdc++.h>
using namespace std;
int main(){
int n,s=0;
cin>>n;
while(n>=1){
s=s+n;
n--;
}
cout<<s;


return 0;}

/**************************************************************
	Problem: 1002
	User: fzy001
	Language: C++
	Result: Accepted
	Time:9 ms
	Memory:2072 kb
****************************************************************/