A,B,C,K = map(int,input().split())

D = {}
A %= 10
B %= 10
C %= 10


from collections import deque
Q = [A,B,C]
Q = deque(Q)

for i in range(4,K+1):
    if i == K:
        print(sum(Q)%10)
        exit()
    elif (Q[0],Q[1],Q[2]) not in D:
        D[(Q[0],Q[1],Q[2])] = i
        S = sum(Q)
        Q.append(S%10)
        a = Q.popleft()
        #print(Q)
    else:
        I = i
        #print(D[(Q[0],Q[1],Q[2])],I)
        break
#print(Q)
#print(D)

K -= D[(Q[0],Q[1],Q[2])]
K %= (I-D[(Q[0],Q[1],Q[2])])
#print(K)
for i in range(K+1):
    S = sum(Q)
    Q.append(S%10)
    a = Q.popleft()
    #print(i,Q)
print(S%10)