#include<iostream>

 #include<cmath>

 #include<cstdio>

 using namespace std;

 double ans,tmp;

 int N1,N2,HP1,HP2,AP1,AP2;

 int main()

 {

     while(cin>>HP1>>HP2>>AP1>>AP2)

     {

         N2=HP1/AP2;        if(HP1%AP2!=)    N2++;

         N1=HP2/AP1;        if(HP2%AP1!=)    N1++;

         ans=pow(0.5,N1);

         //tmp=1.00;

         tmp=;

         for (int i=;i<=N2-;i++)

         {

             //tmp=tmp*(N1-i)/i;

             //ans+=tmp*pow(0.5,N1+i);

             tmp+=log10(N1-1.0+i)-log10(i*1.0);

             ans+=pow(,tmp+(N1+i)*log10(0.5));

         }

         ans=ans*;

         printf("%.4f\n",ans);

     }

 }