#include <stdio.h>

int n;

long comb(int n, int i)
{
	int j;
	long p=1;
	for (j=n-i+1; j<=n; j++) p*=j;
	for (j=2; j<=i; j++) p/=i;
	return p;
}

int main()
{
	long nr=0;
	int i;
	freopen("nunta.in", "r", stdin);
	freopen("nunta.out", "w", stdout);
	scanf("%d\n", &n);
	for (i=0; i<=n/2; i++)
		nr+=comb(n-i, i);
	printf("%ld\n", nr);
	return 0;
}