import java.io.*;
import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner();
        long x = sc.nextLong();
        for (int i = 1; i < 61; i++) {
            if (getPop(x ^ i) == i) {
                System.out.println(x ^ i);
                return;
            }
        }
        System.out.println(-1);
    }
    
    static long getPop(long x) {
        long pop = 0;
        while (x > 0) {
            pop += x % 2;
            x >>= 1;
        }
        return pop;
    }
}

class Scanner {
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    StringTokenizer st = new StringTokenizer("");
    
    public Scanner() throws Exception {
        
    }
    
    public int nextInt() throws Exception {
        return Integer.parseInt(next());
    }
    
    public long nextLong() throws Exception {
        return Long.parseLong(next());
    }
    
    public double nextDouble() throws Exception {
        return Double.parseDouble(next());
    }
    
    public String next() throws Exception {
        while (!st.hasMoreTokens()) {
            st = new StringTokenizer(br.readLine());
        }
        return st.nextToken();
    }
}