#include using namespace std; using VS = vector; using LL = long long; using VI = vector; using VVI = vector; using PII = pair; using PLL = pair; using VL = vector; using VVL = vector; #define ALL(a) begin((a)),end((a)) #define RALL(a) (a).rbegin(), (a).rend() #define SZ(a) int((a).size()) #define SORT(c) sort(ALL((c))) #define RSORT(c) sort(RALL((c))) #define UNIQ(c) (c).erase(unique(ALL((c))), end((c))) #define FOR(i, s, e) for (int(i) = (s); (i) < (e); (i)++) #define FORR(i, s, e) for (int(i) = (s); (i) > (e); (i)--) #define debug(x) cerr << #x << ": " << x << endl const int INF = 1e9; const LL LINF = 1e16; const LL MOD = 1000000007; const double PI = acos(-1.0); int DX[8] = { 0, 0, 1, -1, 1, 1, -1, -1 }; int DY[8] = { 1, -1, 0, 0, 1, -1, 1, -1 }; /* ----- 2018/09/30 Problem: yukicoder 306 / Link: http://yukicoder.me/problems/no/306 ----- */ /* ------問題------ -----問題ここまで----- */ /* -----解説等----- ----解説ここまで---- */ int main() { cin.tie(0); ios_base::sync_with_stdio(false); double x1, y1, x2, y2; cin >> x1 >> y1 >> x2 >> y2; double ans = (y2-y1)/(x1+x2)*x1+y1; cout << fixed << setprecision(10) << ans << "\n"; return 0; }