p,q,r,K = map(int,input().split())
K -= 1
d = {}
x = (p%10,q%10,r%10)
for i in range(10**3+1):
    p,q,r = x
    if x in d.keys():
        break
    else:
        d[x] = i
        d[i] = x
    x = (q,r,(p+q+r)%10)
#print(d)
T = i-d[x]
#print(d[x])
if K < d[x]:
    print(d[K][0])
else:
    K -= d[x]
    print(d[d[x] + K%T][0])