#include <stdio.h>
int n, ans;
void make(int x, int y)
{
    if( x == n ) ans++;
    else if( y == 1 ) make(x+1, 0), make(x+1, 1);
    else make(x+1, 1);
}

int main()
{
    freopen(".10.in","r",stdin);
    freopen(".10.out","w",stdout);
    scanf("%d", &n);
    make(0,1);
    printf("%d\n", ans);
}