#include<bits/stdc++.h>
using namespace std;
long double a,b;
int main(){
    cin>>a>>b;
    cout<<fixed<<setprecision(20)<<100*(a-b)/a;
}/*
00100001000010000100
*/
#include<iostream>
using namespace std;
int main()
{
  float A, B, C;
  float D;
  cin >> A >> B;
  C = A-B;
  D = (C/A)*100.0;
  if(A > B)
    cout << D;
  else
    return -1;
  return 0;
}
  