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: Wrong Answer)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Atcoder
{

    class Atcoderrrrrrr
    {
        static void Main(string[] args)
        {
            long N = long.Parse(Console.ReadLine());
            double ans = 0;
            for (int i = 1; i < N; i++)
            {
                double obj = Math.Pow(i,2);
                if(obj<=N){
                    ans = obj;
                }else{
                    break;
                }
            }
            Console.WriteLine(ans);
        }
    }
}