#include<stdio.h>
int main()
{
    long long int s,k,i,r1,r2;
    scanf("%lld",&k);
    k--;
    r1=k*(k+1)/2;
    r1=1+(r1-1)*2;
    r2=(k+1)*(k+2)/2;
    r2=1+(r2-1)*2;
    for(i=r1+2;i<=r2;i+=2)
        s+=i;
    printf("%lld",s);
}