#include <bits/stdc++.h>

using namespace std;

typedef long long LL;

const int nmax = 1000005; const LL inf = 1e18;


int main(){
   int t1,k1,t2,k2,i,v1,v2;
   bool ok;
//   freopen("txt.in","r",stdin);
//   freopen("txt.out","w",stdout);
    cin >> t1 >> k1 >> t2 >> k2;
   double x1 = t1/k1;
   double x2 = t2/k2;
   cout << (x1+x2)/4;
   return 0;
}