#include<stdio.h>
#include<math.h>
int main()
{
	int n,i;
	double a, b, c;
	scanf("%d", &n);
	a = (1 + sqrt(5)) / 2;
	b = (1 - sqrt(5)) / 2;
	for (i = 1; i < n; i++)
	{
		a *= (1 + sqrt(5)) / 2;
		b *= (1 - sqrt(5)) / 2;
	}
	c = (a - b) / sqrt(5);
	printf("%.2f", c);
	return 0;
}