import collections
d = collections.defaultdict(int)
p,q,r,K = map(int, input().split())
A = [p%10,q%10,r%10]
for  i in range(K-3):
    if d[(A[1],A[2],sum(A)%10)]>0:
        temp = (K-d[(A[1],A[2],sum(A)%10)])%(i+3-d[(A[1],A[2],sum(A)%10)])
        for i in range(temp):
            A = [A[1],A[2],sum(A)%10]
        print(A[-1])
        exit()


    d[(A[1],A[2],sum(A)%10)]=i+3
    A = [A[1],A[2],sum(A)%10]
print(A[-1])