#include <bits/stdc++.h>

#define fst(t) std::get<0>(t)
#define snd(t) std::get<1>(t)
#define thd(t) std::get<2>(t)
#define unless(p) if(!(p))
#define until(p) while(!(p))

using ll = std::int64_t;
using P = std::tuple<int,int>;

double Sx, Sy, Gx, Gy;

int main(){
    std::cin.tie(nullptr);
    std::ios::sync_with_stdio(false);

    std::cin >> Sx >> Sy >> Gx >> Gy;

    double a = (- Gy - Sy) / (Gx - Sx),
        x = Sx - Sy / a;
    printf("%.10f\n", x);
}

/*~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=
*$* WRITER:kakitamasziru/OxOmisosiru *$*
~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=*/
#ifdef LOCAL_JUDGE
#define _GLIBCXX_DEBUG
#endif
#include <stdio.h>
#include <iostream> // cout, endl, cin
#include <string> // string, to_string, stoi
#include <vector> // vector
#include <algorithm> // min, max, swap, sort, reverse, lower_bound, upper_bound
#include <utility> // pair, make_pair
#include <tuple> // tuple, make_tuple
#include <cstdint> // int64_t, int*_t
#include <iomanip> //setprecision
#include <map> // map
#include <queue> // queue, priority_queue
#include <set> // set,multiset
#include <stack> // stack
#include <deque> // deque
#include <math.h>//pow,,,
#include <cmath>//abs,,,
#include <bitset> // bitset
#include <numeric> //accumulate,,,
#include <time.h> //clock
#define endl "\n";
using namespace std;

using PLL = pair<long long,long long>;
using P = pair<int,int>;
const long long INF = 3000000000000000001;
const int inf = 1001001001;
long long MOD = 1000000007;

//Solve N^M. This, mod_pow use Iterative Square Method.
long long mod_pow(long long N, long long M, long long mod) {
    if (M == 0) return 1;
    long long res = mod_pow((N * N) % mod, M / 2,mod);
    //When end-of-a bit is 1, times simple N.
    if (M & 1) res = (res * N) % mod;
    return res %= mod;
}
long long gcd(long long a, long long b) {
    if (b == 0) return a; else return gcd(b, a % b);
}
long long lcm(long long a, long long b) {
    return a / gcd(a, b) * b ;
}
long long get_mod(long long res){
    if(res < 0) res += MOD;
    return res % MOD;
}



int main() {
    ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
    
    long double sx,sy,gx,gy;cin >> sx >> sy >> gx >> gy;
    cout << fixed << setprecision(7) << (gx-sx)*(sy/(sy+gy))+sx << endl;
}