def main():
    import sys
    X = int(sys.stdin.readline().strip())
    max_m = 60
    for M in range(1, max_m + 1):
        N = X ^ M
        if 1 <= N <= 2 * 10**18 and bin(N).count('1') == M:
            print(N)
            return
    print(-1)

if __name__ == "__main__":
    main()