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 Common Lisp (SBCL 1.1.14) (judge verdict: Wrong Answer)

(let ((n (read)))
  (loop for i from n downto 0
        for s = (sqrt i)
        when (= s (floor s)) do
        (format t "~A~%" i)
        (return)))