#include<bits/stdc++.h>
using namespace std;
#define pi 3.1415926;
main(){
	long long n,m;
	while(cin>>n>>m){
		if(n==0&&m==0)break;
		double ans=0;
		for(double i=n;i<=m;++i)ans+=(1/i/i);
		printf("%.6lf",ans);
		cout<<endl;
	}
	
	
}