#include using namespace std; // 基本テンプレート struct cww{cww(){ios::sync_with_stdio(false);cin.tie(0);}}star; #define P(x) cout << (x) << endl #define p(x) cout << (x) #define all(c) (c).begin(), (c).end() #define rall(c) (c).rbegin(), (c).rend() #define mat(type, c, m, n) vector> c(m, vector(n));for(auto& r:c)for(auto& i:r)cin>>i; #define rep(i,a,n) for(int i=(a), i##_len=(n); in; --i) #define each(x,y) for(auto &(x):(y)) #define perm(c) sort(all(c));for(bool c##p=1;c##p;c##p=next_permutation(all(c))) #define cauto const auto& #define UNIQUE(v) v.erase( unique(all(v)), v.end() ); #define len(x) ((int)(x).size()) #define length(a) (sizeof(a)/sizeof(a[0])) template inline bool inside(T y, T x, T h, T w) { return 0 <= y && y < h && 0 <= x && x < w; }; // デバッグ用 template inline void print(T t){cout << t << endl;} template inline void print(H h, T... t){cout << h << " ";print(t...);} #define dbg(v) for(auto i : v) { cout << i << " "; } cout << endl; // 型 typedef long long ll; typedef vector vi; typedef vector vd; typedef vector vll; typedef vector vs; typedef vector vb; // 定数 #define PI acos(-1.0) //constexpr int EPS = (1e-9); //constexpr int INF = 100000000; // 4近傍 //constexpr int dx[] = {1, 0, -1, 0}; //constexpr int dy[] = {0, 1, 0, -1}; // 8近傍 //constexpr int dy[]={0,0,1,-1,1,1,-1,-1}; //constexpr int dx[]={1,-1,0,0,1,-1,1,-1}; //constexpr int MAX = 1005; //ll mod = 1000007; int main() { cout << setprecision(12) << fixed; ll l, r, d, w; cin >> l >> r >> d >> w; P(d * w / (double)(l + r) ); return 0; }