p,q,r,K = map(int,input().split()) p %= 10 q %= 10 r %= 10 s = set() A = [p,q,r] while (p,q,r) not in s: s.add( (p,q,r) ) p,q,r = q,r,(p+q+r) % 10 A.append(r) X = len(A)-3 print (A[(K-1) % X])