#include <stdio.h>

main()
{
	float s, s0;
	int i, a, b, t;

	a = 1;
	b = 2;
	s = s0 = (float)b/(float)a;
	for (i = 2; i <= 20; i++) {
		t = a;
		a = b;
		b += t;
		s0 = (float)b/(float)a;
		s+=s0;
	}
	printf("%f\n", s);
	return 0;
}