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++ (GCC 9.2.1) (judge verdict: Accepted)

#include <iostream>
#include<set>
#include<vector>
#include<string>
#include<iterator>
#include<iomanip>
#include<cmath>
#include<map>
#include<string.h>
#include<algorithm>

using namespace std;
void ll(){
	std::ios_base::sync_with_stdio(0);
	cin.tie(NULL);
	cout.tie(0);
}

int main() {

	ll();
	
	long long a,c=0,i=0;
	double  b;
	cin >> a;
	b = sqrt(a);
	c = sqrt(a);
	i = a;
	if ((b - c) == 0)
		cout << a << endl;
	else
	{
		while (true)
		{
			i--;
			b = sqrt(i);
			c = sqrt(i);
			if ((b - c) == 0)
			{
				cout << i << endl;
				return 0;
			}
		}
	}

}