from collections import defaultdict 

def main():
    p,q,r,k = map(int,input().split())
    A = [p%10,q%10,r%10]
    dic = defaultdict(int)
    dic[tuple(A)] = 1 #1スタート
    dic1 = defaultdict(int)
    num = 2
    while True:
        val = A[-1] + A[-2] + A[-3]
        val %= 10
        nxt = (A[-2], A[-1], val)
        A.append(val)
        if nxt in dic:
            loop_start = dic[nxt]
            loop_last = num - 1 
            break
        else:
            dic[nxt] = num
            num += 1
    #print(dic,loop_start,loop_last)
    loop_len = loop_last - loop_start + 1 
    if k <= len(A):
        print(A[k-1]);exit()
    amari = loop_start - 1
    idx = (k - amari) % loop_len + amari - 1
    #print(idx)
    print(A[idx])

if __name__ == '__main__':
    main()