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: Accepted)

n = gets.to_i

n.downto(1) do |i| # 1回繰り返す毎に1ずつ数値は減少
  if (i ** 0.5 ) == (i ** 0.5 ).to_i # 計算式これでいいのかわからない
    puts i
    break  # １コで終了
  end
end

# puts ans