import sys
p,q,r,K = map(int,input().split())

if K < 4:
    print([p,q,r][K-1])
    sys.exit()
K -= 4
K %= 124
A = [p%10,q%10,r%10]
for i in range(K+1):
    a = sum(A) % 10
    A = A[1:] + [a]
print(a)