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 5.4.1) (judge verdict: Wrong Answer)

#include <stdio.h>
#include <string.h>
#include <math.h>

int main()
{
    char a[3] = {}, b[3] = {}, flg;
    for(int j = 0; j<3; j++)
        scanf("%c", &a[j]);
    scanf("%c", &flg);
    for(int j = 0; j<3; j++)
        scanf("%c", &b[j]);
    if((a[0] == b[2]) && (a[1] == b[1]) && (a[2] == b[0]))
        printf("YES");
    else
        printf("NO");

}