#include <stdio.h>
int main()
{
	int n,i;
    float fn[100] = {1.00,1.00,2.00};
	scanf("%d",&n);
	for(i=3;i<=n;i++)
	{
	fn[i] = fn[i-1] + fn[i-2];
	}
	printf("%.2f",fn[n-1]);
	return 0;
 }