# import sys; input = sys.stdin.buffer.readline
# sys.setrecursionlimit(10**7)
from collections import defaultdict
con = 10 ** 9 + 7; INF = float("inf")

def getlist():
	return list(map(int, input().split()))

#処理内容
def main():
	A, B, X, Y = getlist()
	if A * Y == B * X:
		print(X + Y)
	elif A * Y > B * X:
		print(X * (A + B) / A)
	else:
		print(Y * (A + B) / B)



if __name__ == '__main__':
	main()