#include using namespace std; typedef long long ll; #define loop(i,a,b) for(i=a;i=b;i--) #define vi vector #define vl vector #define vii vector< vector > #define vll vector< vector > #define vs vector const int inf=1000000001; const ll INF=1e16; #define MOD 1000000007 #define mod 1000000009 #define pi 3.14159265358979323846 int main(){ long double v1,v2,w,d; cin>>v1>>v2>>d>>w; long double t; t=d/(v1+v2); cout<