#include<cstdio>
using namespace std;
int main()
{
	int n;
	scanf("%d",&n);
	long long a=0,b=1,c;
	for (int i=2;i<=n;i++)
	{
		c = b;
		b = a+b;
		a = c;
	}
	printf("%.2lf",double(b));
	return 0;
}