3tomcha

# coding: utf-8
# Your code here!

import math

while True:
    n = int(input())
    if n == 0:
        break
    s = list(map(int, input().split()))

3tomcha

# coding: utf-8
# Your code here!

import math
x1, y1, x2, y2 = map(float, input().split())
result = math.sqrt( (x2-x1) * (x2-x1) + (y2-y1) * (y2-y1) )
print(result)

3tomcha

function __construct($orientation='P', $unit='mm', $format='A4')
{

3tomcha

# coding: utf-8
# Your code here!

# ITP1_8_D

N=input()
N=N*2
S=input()

if S in N:

3tomcha

# coding: utf-8
# Your code here!
# ITP1_8_C
import sys


alphabet={chr(i) : 0 for i in range(97, 97+26)}
R=""
for text in sys.stdin:
    R += text.lower()

3tomcha

# coding: utf-8
# Your code here!

# ITP1_7_B


# 小中大の順に
# a<b<cとする

import math

3tomcha

# coding: utf-8
# Your code here!

# ITP1_7_A


def judge(point,re_exam_point):
    if point>=80:
        return "A"
    elif 65 <= point < 80:

3tomcha

# coding: utf-8
# Your code here!

# ITP1_6_D

matrix=list()
col=list()
y,x=map(int,input().split())

for _ in range(y):

3tomcha

# coding: utf-8
# Your code here!

print("test4")

3tomcha

# coding: utf-8
# Your code here!
# TP1_2_D

# 5 4 2 2 1
# 22 - 33
# 3 < 5　かつ　3<4だからOK

# 5 4 2 4 1
# 24 - 35