SGU111 Very simple problem

import java.util.*;
import java.math.*;

public class Solution {
public static void main(String args[]) {
Scanner in = new Scanner(System.in);

BigInteger X = in.nextBigInteger();

BigInteger L = BigInteger.valueOf(1);
BigInteger R = BigInteger.valueOf(10).pow(500);

while (L.compareTo(R) <= 0) {
BigInteger M = L.add(R).divide(BigInteger.valueOf(2));
if (M.pow(2).compareTo(X) <= 0) {
L = M.add(BigInteger.valueOf(1));
} else {
R = M.subtract(BigInteger.valueOf(1));
}
}

System.out.println(R);
}
}