# 第一行输入
import math

x1, y1 = map(float, input().split())
# 第二行输入
x2, y2 = map(float, input().split())
# 01计算x1,和x2的差值
x_differ = abs(x1 - x2)
y_differ = abs(y1 - y2)
m_differ = x_differ + y_differ
d_differ = math.sqrt(x_differ ** 2 + y_differ ** 2)
result = m_differ - d_differ
print(result)

01:先要知道x1,x2输入的值

02:算出差的绝对值

03:计算相加的和,和平方的值

04:计算对应的值