import sys
import math
from collections import deque,Counter
#sys.setrecursionlimit(10**7)
int1=lambda x: int(x)-1

mi=lambda :map(int,input().split())
li=lambda :list(mi())
mi1=lambda :map(int1,input().split())
li1=lambda :list(mi1())
mis=lambda :map(str,input().split())
lis=lambda :list(mis())

from collections import defaultdict
"""
d=defaultdict(int) #初期値 0
d=defaultdict(lambda:1) #初期値 1
"""

mod=10**9+7
Mod=998244353
INF=10**18
ans=0

p,q,r,k=mi()
p%=10
q%=10
r%=10
a=[(p,q,r)]
while True:
  p,q,r=q,r,(p+q+r)%10
  if (p,q,r) in a:
    x=a.index((p,q,r))
    y=len(a)
    if y>k-3:
      print(a[k-3][2])
      exit()
    m=k-x-3
    n=m%(y-x)
    print(a[x+n][2])
    exit()
  else:
    a.append((p,q,r))