import sys
import numpy as np

read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline

def from_read(dtype=np.int64):
    return np.fromstring(read().decode(), dtype=dtype, sep=' ')

def from_readline(dtype=np.int64):
    return np.fromstring(readline().decode(), dtype=dtype, sep=' ')

def read_matrix(N, M, dtype=np.int64):
    matrix = np.empty((N, M), dtype=dtype)
    for i in range(N):
        matrix[i] = from_readline(dtype)
    return matrix

def matrix_pow(A, N):
    res = np.eye(len(A), dtype=np.int64)
    while N:
        if N & 1:
            res = res @ A % 10
        A = A @ A % 10
        N >>= 1
    return res

def solve(p, q, r, K):
    A = np.array([[1, 1, 1], [1, 0, 0], [0, 1, 0]])
    B = matrix_pow(A, K - 3)
    res = B[0, 0] * r + B[0, 1] * q + B[0, 2] * p
    res %= 10
    return res

def main():
    p, q, r, K = from_readline()
    print(solve(p, q, r, K))

if __name__ == "__main__":
    main()