#include <cstdio>
#include <cstdlib>
#include <iostream>
#include <string>
#include <cmath>
#include <algorithm>
#include <vector>
#include <queue>
#include <stack>

using namespace std;



int main(){
    long long n,max_n=0,sum;
    
    scanf("%lld",&n);
    
    for(int i=1;i<=n;i++){
        sum=i+(n-i)*(i+1);
        if(max_n<sum)
            max_n=sum;
    }
    
    printf("%lld\n",max_n);
    
    return 0;
}