#include <bits/stdc++.h>

#define REP(i, n) for(i64 i = 0; i < n; ++i)
#define RREP(i, n) for(i64 i = n - 1; i >= 0; --i)
#define FOR(i, a, b) for(auto i = a; i != b; ++i)
#define ALL(v) (v).begin(), (v).end()

using namespace std;

using i64 = int_fast64_t;
using u64 = uint_fast64_t;
using f64 = double;
using p64 = pair<i64, i64>;

const string ln = "\n";
const i64 dx[4] = {1, 0, -1, 0};
const i64 dy[4] = {0, 1, 0, -1};
const i64 inf = 1e18;

i64 Sx, Sy, Gx, Gy;

int main() {
    cin >> Sx >> Sy >> Gx >> Gy;
    f64 ans = Gx - (f64)Gy * (Gx - Sx) / (Gy + Sy);
    cout << fixed << setprecision(10) << ans << ln;
}
#include<stdio.h>
#include<algorithm>
using namespace std;
int main()
{
    double a,b,c,d;
    double x,k;
    double s,e;
    scanf("%lf%lf%lf%lf",&a,&b,&c,&d);

    x=-d*(c-a)/(d+b)+c;
    printf("%lf",x);


}