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 <algorithm>
#include <bitset>
#include <cctype>
#include <climits>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <deque>
#include <functional>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <numeric>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <utility>
#include <vector>

using namespace std;

#define FOR(i, first, last) for (int i = (first); i < (last); ++i)
#define REP(i, n) FOR(i, 0, n)
#define CLR(a) memset((a), 0, sizeof(a))
#define DUMP(x) std::cerr << #x << " = " << (x) << std::endl;

inline int to_int(string s) {
  int v;
  istringstream sin(s);
  sin >> v;
  return v;
}
template <class T> inline string to_string(T x) {
  ostringstream sout;
  sout << x;
  return sout.str();
}

typedef unsigned long long ull;
typedef unsigned long ul;

int main() {
  ull N;
  cin>>N;
  
  ull m = (ull)std::sqrt(N);
  cout << m*m << endl;

  return 0;
}