#include <stdio.h>


int main() {
    int n;
    scanf("%d",&n);
    int re = (4+3*(n-1));
    int re1;
    if(re%2==0)
    {
        re1 = re/2*n;
    }else if(re%2==1)
    {
        re1 = re/2*n+n/2;
    }
    
    printf("%d",re1);
}