#include<iostreaam>
using namespace std;
int main(){
    double pr,pi;
    cin>>pr>>pi;
    try{
        if(pi==0){
            throw 0;
        }
        double result=pr/pi;
        cout<<fixed<<setprecision(2)<<result;
    }
    catch(int x){
        cout<<-1;
    }
    return 0;
}