include

include

using namespace std;

int main(){

int n,m;
double a;

while(cin>>n>>m&&(n!=0||m!=0)){
    a=0;
    for(int i=n;i<=m;i++){
        a+=1.0/i/i;
    }
    cout<<fixed<<setprecision(6)<<a<<endl;
}

return 0;

}