p,q,r,K = map(int,input().split()) mem = [[[-1]*10 for _ in range(10)] for _ in range(10)] a,b,c = p%10, q%10, r%10 mem[a][b][c] = 0 rev = {0:(a,b,c)} i = 1 while 1: d = (a+b+c)%10 a,b,c = b,c,d if mem[a][b][c] >= 0: r = i break mem[a][b][c] = i rev[i] = (a,b,c) i += 1 K -= 4 a,b,c = rev[K%r] print((a+b+c)%10)