import sys
input = lambda :sys.stdin.readline()[:-1]
ni = lambda :int(input())
na = lambda :list(map(int,input().split()))
sys.setrecursionlimit(10**7)
yes = lambda :print("yes");Yes = lambda :print("Yes")
no = lambda :print("no");No = lambda :print("No")
#######################################################################
p,q,r,K = na()
mod = 10
def mat_mul(a,b):
    n,m,l=len(a),len(b[0]),len(b)
    c=[[0]*m for _ in range(n)]
    for i in range(n):
        for k in range(l):
            for  j in range(m):
                c[i][j]=(c[i][j]+a[i][k]*b[k][j])%mod
    return c
 
#a^nの計算
def mat_pow(a,n):
    m=len(a)
    b=[[0]*m for _ in range(m)]
    for i in range(m):
        b[i][i]=1
    while n>0:
        if n&1:
            b=mat_mul(b,a)
        a=mat_mul(a,a)
        n>>=1
    return b
#print(z)
a = [p%10,q%10,r%10]
if K>=4:
    z = [[1,1,1],[1,0,0],[0,1,0]]
    ans=mat_pow(z,K-3)
    print(sum([ans[0][i]*a[2-i]for i in range(3)])%10)
    #print(ans)
    #print(b)
else:
    print(a[K-1])