#include<bits/stdc++.h>
using namespace std;
int main(){
    int s=1,h=0,n;
    cin>>n;
    while(s<=n){  
        h=s+h;  
        s++; 
    }
    cout<<h;
     
    return 0;
}
/**************************************************************
	Problem: 1002
	User: binzicheng
	Language: C++
	Result: Accepted
	Time:18 ms
	Memory:2072 kb
****************************************************************/