#include <stdio.h>
#include <math.h>

double binet(char n)
{
	double a,b;
	a = pow( ((1.0+sqrt(5)) / 2.0) , 1.0*n);
	b = pow( ((1.0-sqrt(5)) / 2.0) , 1.0*n);
	return (a-b) / sqrt(5);
}

int main(void)
{
	char n;
	scanf("%hhd",&n);

	printf("%.f\n",binet(n+1));
	
	return 0;
}