# ###
#Concealed Square
#
# Problem 206
# Find the unique positive integer whose square has the form 1_2_3_4_5_6_7_8_9_0,
# where each “_” is a single digit.
# ###


import math
from itertools import count


for n in count(int(math.sqrt(1020304050607080900)) - 1):
    s = str(n * n)
    if s[0] == "1" and s[2] == "2" and s[4] == "3" and s[6] == "4" and s[8] == "5" and s[10] == "6" and s[12] == "7" and s[14] == "8" and s[16] == "9" and s[18] == "0":
        print(">>>", n)
        break