import java.util.Scanner;
 
public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        long x = sc.nextLong();
 
        for (long y = 1; y <= (long) 1e6; y++) { // 为了效率，只枚举到1e6，一般足够找出最小的y
            long z = x ^ y;
            if (z == 0) continue;
            if (x % z == 0 && y % z == 0) {
                System.out.println(y);
                return;
            }
        }
 
        System.out.println(-1);
    }
}
 

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

Ng==

6