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 C# (Mono-mcs 6.8.0.105) (judge verdict: Accepted)

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Runtime.CompilerServices;
using System.Text;
using System.Text.RegularExpressions;
using System.Threading.Tasks;

namespace AtCoder
{
    public class QuestionA
    {
        public static void Main(string[] args)
        {
            double result = 0;

            // 整数の入力
            long n = int.Parse(Console.ReadLine());

            for (int i = 0; i < n; ++i) {
                var m = n - i;

                double x = Math.Sqrt((double)m);
                if (x == (int)x) {
                    result = m;
                    break;
                }
            }

            Console.WriteLine(result);
        }
    }
}