# -*- coding:utf-8 -*-
if __name__ == "__main__":
	a,b,x,y = map(float,raw_input().split())
	need = min(x,y) * max(a,b) / min(a,b)
	if need > max(x,y):
		print max(x,y) * min(a,b) / max(a,b) + max(x,y)
	else:
		print min(x,y) + need