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 4.6.2.0) (judge verdict: Runtime Error)

using System;

namespace AroundSquare
{
    class Program
    {
        static void Main(string[] args)
        {
            int N = int.Parse(Console.ReadLine());
            int[] x = new int[N];
            int[] y = new int[N * N];

            for(int i = 0; i < N; i++)
            {
                x[i] = i + 1;
                y[i] = x[i] * x[i];
                if(y[i] > N)
                {
                    Console.WriteLine(y[i - 1]);
                    break;
                }
            }
        }
    }
}