#include<iostream>

include<iomanip>

using namespace std; using std::setprecision;

int main() { int a; float b; cin>>a; if(a>0) { cin>>b; cout<<"\t"; if(b>0||b>0) { if(a%5==0) { if(b>a) { cout<<setprecision(2)<<(b-a-0.5); }} else cout<<b; } } return 0; }