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++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include<iostream>
#include<cmath>
using namespace std;

int
main()
{
	long long n, output;
	double m;
	cin.tie(0);
	ios::sync_with_stdio(false);
	cin >> n;
	for (long long i = n; i >= 1; i--) {
		m = sqrt(i);
		if (pow(m + 1, 2.0) - i == 2 * m + 1) {
			output = i;
			break;
		}
	}
	cout << output << endl;
}