class INPUT:
  def __init__(self):
    self._l=open(0).read().split()
    self._length=len(self._l)
    self._index=0
    return

  def stream(self,k=1,f=int,f2=False):
    assert(-1<k)
    if self._length==self._index or self._length-self._index<k:
      raise Exception("There is no input!")
    elif f!=str:
      if k==0:
        ret=list(map(f,self._l[self._index:]))
        self._index=self._length
        return ret
      if k==1 and not f2:
        ret=f(self._l[self._index])
        self._index+=1
        return ret
      if k==1 and f2:
        ret=[f(self._l[self._index])]
        self._index+=1
        return ret
      ret=[]
      for _ in [0]*k:
        ret.append(f(self._l[self._index]))
        self._index+=1
      return ret
    else:
      if k==0:
        ret=list(self._l[self._index:])
        self._index=self._length
        return ret
      if k==1 and not f2:
        ret=self._l[self._index]
        self._index+=1
        return ret
      if k==1 and f2:
        ret=[self._l[self._index]]
        self._index+=1
        return ret
      ret=[]
      for _ in [0]*k:
        ret.append(self._l[self._index])
        self._index+=1
      return ret
pin=INPUT().stream


#pin(number[default:1],f[default:int],f2[default:False])
#if number==0 -> return left all
#listを変数で受け取るとき、必ずlistをTrueにすること。

from collections import Counter
def main():
  p,q,r,K=pin(4)
  p%=10
  q%=10
  r%=10
  A=[p,q,r]
  S=Counter()
  for i in range(K-3):
    t=(A[i]+A[i+1]+A[i+2])%10
    #print(S[(A[i],A[i+1],A[i+2])])
    if S[(A[i],A[i+1],A[i+2])]!=0:
      u=S[(A[i],A[i+1],A[i+2])]-1
      loop=i-u
      left=K-i-1
      v=left%loop
      print(A[u+v])
      #print(A)
      #print(u,v)
      #print(i,len(A))
      #print(left,loop)
      return
    S[(A[i],A[i+1],A[i+2])]=i+1
    A.append(t)
  print(A[-1])
  #print(A)
  return

main()