import math
x1 = float(input())
y1 = float(input())
x2 = float(input())
y2 = float(input())
d = math.sqrt((x2 - x1)**2 + (y2 - y1)**2)
print(d)
aW1wb3J0IG1hdGgKCngxID0gZmxvYXQoaW5wdXQoKSkKeTEgPSBmbG9hdChpbnB1dCgpKQp4MiA9IGZsb2F0KGlucHV0KCkpCnkyID0gZmxvYXQoaW5wdXQoKSkKCmQgPSBtYXRoLnNxcnQoKHgyIC0geDEpKioyICsgKHkyIC0geTEpKioyKQpwcmludChkKQo=