#include <stdio.h>

int main()
{
	int n,m;
	int kase = 0;
	
	while(scanf("%d%d",&n,&m) == 2 && ( n || m ))
	{
		double sum = 0;
		for(int i=n;i<=m;i++){
			sum += (double) 1/i/i;
		}
		printf("Case %d: %.5f\n",++kase,sum);
	}
	
	return 0;
}