HDOJ 1395 2^x mod n = 1

import java.util.Scanner;

public class Main{
public static void main(String[] args) {

Scanner sc = new Scanner(System.in);
while (sc.hasNext()) {
int n = sc.nextInt();
if (n%2==0||n==1) {
System.out.println("2^? mod "+n+" = 1");
continue;
}
int num = 2;
int x = 1;
while (num%n!=1) {
num = num << 1;
num = num%n;
x++;
}
System.out.println("2^"+x+" mod "+n+" = 1");
}
sc.close();
}
}