Problem:
Score : 200 points

Problem Statement

Find the largest square number not exceeding N. Here, a square number is an integer that can be represented as the square of an integer.

Constraints

1 \leq N \leq 10^9

N is an integer.

Input

Input is given from Standard Input in the following format:

N

Output

Print the largest square number not exceeding N.

Sample Input 1

10

Sample Output 1

9

10 is not square, but 9 = 3 × 3 is. Thus, we print 9.

Sample Input 2

81

Sample Output 2

81

Sample Input 3

271828182

Sample Output 3

271821169

Solution in Ruby (2.3.3) (judge verdict: Runtime Error)

lines = $stdin.read
array = lines.split("\n")

N = array[0].to_i

def ceil_power(n, elem)
  #puts "n = #{n}, #{n*n} =< #{elem} =< #{(n+1)*(n+1)} ?"

  if n*n <= elem and elem == (n+1)*(n+1)
    n+1
  elsif n*n <= elem and elem <= (n+1)*(n+1)
    n
  else
    ceil_power(n+1, elem)
  end
end

n = 1
ans = ceil_power(n,N)
puts ans**2