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: Accepted)

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef unsigned long long llu;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)

int main() {
    llu n;
    cin >> n;

    llu ans = 1;
    for (llu i = 1; i < n; i++) {
        if ((llu)(i * i) <= (llu)n) {
            ans = (llu)(i * i);
        }
        else 
            break;
    }

    cout << ans << endl;
}