a,b,c,k=map(int,input().split())
a%=10
b%=10
c%=10
k-=3
v=[[[-1]*10 for i in range(10)] for j in range(10)]
l=0
r=0
q=[(a,b,c)]
v[a][b][c]=0
while 1:
  a,b,c=q[-1]
  aa,bb,cc=b,c,(a+b+c)%10
  if v[aa][bb][cc]==-1:
    r+=1
    v[aa][bb][cc]+=v[a][b][c]+1
    q+=[(aa,bb,cc)]
  else:
    l=v[aa][bb][cc]
    break
if k<=r:
  print(q[k][-1])
else:
  print(q[(k-l)%(r-l+1)][-1])