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 PHP (5.6.30) (judge verdict: Accepted)

<?php
    fscanf(STDIN, "%d", $n);
    $ok = 1;
    $ng = $n + 1;
    while($ok + 1 < $ng){
        $mid = floor(($ok + $ng) / 2);
        if($mid * $mid <= $n){
            $ok = $mid;
        }else{
            $ng = $mid;
        }
    }
    echo ($ok * $ok)."\n";
?>