#64 xor
#xorf
import math
def tw(n):
    t=1.0
    k=0
    while t<n:
        t*=2
        k+=1
    #    print (k)
    t/=2
    tt=[]
    while n>0:    
        q=math.floor(n/t)
 #       print (q)
        tt.append(q)
     #   print (tt)
        q*=t
        t/=2
        n-=q
    #    print (n)
        k-=1
  #  print (k)
    while k>0:
        tt.append(0)
     #   print (tt)
        k-=1
    return tt
def twe(li):
    en=0.0
    t1=1
    i=len(li)-1
    while i>=0:
        en+=t1*li[i]
        t1*=2
        i-=1
    return en
def xor(l0,l1):
    l2=[]
    for i in range(len(l1)):
        if l0[i]!=l1[i]:
            l2.append(1)
        else:
            l2.append(0)
    return l2
F0,F1,N=(float(i) for i in input().split())
if N==0.0:
    print(F0)  
elif N==1.0:
    print(F1)
else:
    F0=tw(F0)
    F1=tw(F1)
    Di=len(F0)-len(F1)
    if Di>0:
        Dk=[0]*Di
        F1=Dk+F1
    elif Di<0:
        Di*=-1
        Dk=[0]*Di
        F0=Dk+F0
while N>1.0:
    F2=xor(F0,F1)
    F0=F1
    F1=F2
    N-=1
print(int(twe(F1)))