# coding:utf-8

def main():
    xa, ya = map(int, input().split())
    xb, yb = map(int, input().split())
    if ya>yb:
        xa, xb = xb, xa
        ya, yb = yb, ya
    ub = yb
    lb = ya
    mid = (lb+ub)/2
    for i in range(10000000):
        if yb == mid or ya == mid:
            break
        if xb/(yb-mid)>xa/(mid-ya):
            mid = (mid+lb)/2
        elif xb/(yb-mid)<xa/(mid-ya):
            mid = (mid+ub)/2
        else:
            break
    print(mid)

main()