#include<bits/stdc++.h> #define ll long long #define pb push_back #define mp make_pair #define mod 1000000007 #define fast ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0); #define F first #define S second #define pii pair<int,int> #define afor(i,a,b) for(int i=a;i<b;++i) #define bfor(i,a,b) for(int i=a;i>=b;--i) #define print(A,j,k) for(int ii=j;ii<k;ii++)cout<<A[ii]<<" ";cout<<"\n" #define all(v) v.begin(),v.end() #define ps cout<<"YES\n"; #define PI 3.14159265358979323846264338 #define CASES int t;cin>>t;while(t--) //ans = a ? b : c; // to simplify: if (a) ans = b; else ans = c; //if(x&1)-->odd else even. //freopen("in.txt","r",stdin); //freopen("out.txt","w",stdout); using namespace std; int main() { long double t1,k1,t2,k2; cin>>t1>>k1>>t2>>k2; cout<<fixed<<setprecision(6)<<(t1*t2)/(k1*t2+k2*t1)<<"\n"; return 0; }