p,q,r,k=map(int,input().split())
k-=3
m=9<<9
for i in range(min(k,m)):
    p,q,r=q,r,(p+q+r)%10
k-=m
if k>0:
    c=0
    t=(p,q,r)
    while k>0:
        p,q,r=q,r,(p+q+r)%10
        c+=1
        k-=1
        if (p,q,r)==t:
            break
    k%=c
    while k>0:
        p,q,r=q,r,(p+q+r)%10
        c+=1
        k-=1
print(r)