#!/usr/bin/env python3
# from typing import *

import sys
import io
import numpy as np
import math
import collections
import decimal
import itertools
import bisect
import heapq


def input():
    return sys.stdin.readline()[:-1]


# sys.setrecursionlimit(1000000)

# _INPUT = """86 91 20 1001
# """
# sys.stdin = io.StringIO(_INPUT)

INF = 10**10


def solve(p, q, r, K):

    N = K-3
    A = np.matrix([[1, 1, 1], [1, 0, 0], [0, 1, 0]])
    M = A
    An = np.identity(M.shape[0], dtype=object)
    while N:
        if N & 1:
            An = np.mod(An * M, 10)
        M = np.mod(M * M, 10)
        N >>= 1
    v = An * np.array([[r], [q], [p]])
    return v[0, 0] % 10

p, q, r, K = map(int, input().split())
print(solve(p, q, r, K))