X = int(input())

if X==0:
    print(-1)
    exit()
    
for i in range(100):
    if (X>>i)&1:
        msb = i
    
for M in range(msb+2):
    N = X^M
    M2 = 0
    
    for i in range(100):
        if (N>>i)&1:
            M2 += 1
    
    if M==M2:
        print(N)
        exit()

print(-1)