#include <bits/stdc++.h>
#include <sys/time.h>
#pragma GCC optimize "O3,omit-frame-pointer,inline"
#define REP(i, n) for(int i = 0;i < n;i++)
#define ll long long
using namespace std;
//typedef vector<unsigned int>vec;
//typedef vector<ll>vec;
//typedef vector<vec> mat;
typedef pair<int, int> P;
typedef pair<ll,ll> LP;
//const int dx[8] = {1, 0, -1, 0, 1, -1, -1, 1};
//const int dy[8] = {0, 1, 0, -1, 1, 1, -1, -1};
const int INF = 1000000000;
const ll LINF = 1000000000000000000;//1e18
const ll  MOD = 1000000007;
const double PI = acos(-1.0);
const double EPS = 1e-10;

template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return true; } return false; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return true; } return false; }
//template<class T> inline void add(T &a, T b){a = ((a+b) % MOD + MOD) % MOD;};


constexpr ll CYCLES_PER_SEC = 2800000000;
constexpr double TL = 1990;
double get_ms() { struct timeval t; gettimeofday(&t, NULL); return (double)t.tv_sec * 1000 + (double)t.tv_usec / 1000; }
constexpr int dh[4] = {-1, 0, 1, 0};
constexpr int dw[4] = {0, 1, 0, -1};
constexpr char MOVE[4] = {'U', 'R', 'D', 'L'};

uint32_t XorShift(void) {
	static uint32_t x = 123456789;
	static uint32_t y = 362436069;
	static uint32_t z = 521288629;
	static uint32_t w = 88675123;
	uint32_t t;

	t = x ^ (x << 11);
	x = y; y = z; z = w;
	return w = (w ^ (w >> 19)) ^ (t ^ (t >> 8));
}

double Prob(void){
	double ret = (double)XorShift() / UINT_MAX;
	return ret;
}


namespace AHC004{
    int N, M;
    vector<string> S;
    void input(){
        cin >> N >> M;
        S.resize(M);
        REP(i,M) cin >> S[i];
    }


    void output(){
        REP(i,N) cout << string(N, 'A') << endl;
    }

    void main(){
        input();
        output();
    }
}

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    AHC004::main();
}
#include<algorithm>
#include<bitset>
#include<cmath>
#include<complex>
#include<deque>
#include<functional>
#include<iomanip>
#include<iostream>
#include<iterator>
#include<map>
#include<numeric>
#include<queue>
#include<set>
#include<stack>
#include<string>
#include<unordered_map>
#include<unordered_set>
#include<utility>
#include<vector>
#include<chrono>
using namespace std;
#define rep(i,n) for(int i=0; i<(n); i++)
#define FOR(i,x,n) for(int i=x; i<(n); i++)
#define vint(a,n) vint a(n); rep(i, n) cin >> a[i];
#define vll(a,n) vll a(n); rep(i, n) cin >> a[i];
#define ALL(n) begin(n),end(n)
#define RALL(n) rbegin(n),rend(n)
#define MOD (1000000007)
// #define MOD (998244353)
#define INF (2e9)
#define INFL (2e18)

typedef long long ll;
typedef unsigned int ui;
typedef unsigned long long ull;
using vint=vector<int>;
using vll=vector<ll>;
using vbool=vector<bool>;
template<class T>using arr=vector<vector<T>>;
template<class T>int popcount(T &a){int c=0; rep(i, 8*(int)sizeof(a)){if((a>>i)&1) c++;} return c;}
template<class T>void pl(T x){cout << x << " ";}
template<class T>void pr(T x){cout << x << endl;}
template<class T>void prvec(vector<T>& a){rep(i, a.size()-1){pl(a[i]);} pr(a.back());}
template<class T>void prarr(arr<T>& a){rep(i, a.size()) if(a[i].empty()) pr(""); else prvec(a[i]);}
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }

int main()
{
    double a, b, x, y; cin >> a >> b >> x >> y;
    double ans = a + (x-a)*b/(y+b);
    printf("%.20lf\n", ans);
    return 0;}