#include<stdio.h>
long n,x,x1,x2,x3,x4,nrt,p;
int main()
{
    freopen("fractii.in","r",stdin);
    freopen("fractii.out","w",stdout);
    scanf("%ld",&x);
    if(x==1)
            printf("3");
    else if(x==2)
         printf("7");
    else if(x==3)
         printf("11");
    else if(x==4)
         printf("19");
    else
    {
        nrt=3;
        x1=4;
        nrt+=x1;
        x2=4;
        nrt+=x2;
        x3=8;
        nrt+=x3;
        p=3;
        while(p<x-1)
        {
                   p++;
                   if(p%2==0)
                   {
                             x4=x2;
                             x1=x2;
                             x2=x3;
                             x3=x4;
                             x4=0;
                             nrt+=x3;
                   }
                   else
                   {
                       x4=x2+4;
                       x1=x2;
                       x2=x3;
                       x3=x4;
                       x4=0;
                       nrt+=x3;
                   }
        }
        printf("%ld",nrt);
    }
    return 0;
}