p, q, r, K = map(int, input().split())

mod_p = p % 10
mod_q = q % 10
mod_r = r % 10

if K == 1:
    print(mod_p)
elif K == 2:
    print(mod_q)
elif K == 3:
    print(mod_r)
else:
    current_state = (mod_p, mod_q, mod_r)
    prev_states = {current_state: 3}
    step = 3  # Last processed step is 3 (A3)
    found_cycle = False

    while step < K:
        step += 1
        a, b, c = current_state
        next_val = (a + b + c) % 10
        new_state = (b, c, next_val)
        if new_state in prev_states:
            # Cycle detected
            cycle_start = prev_states[new_state]
            cycle_length = step - cycle_start
            # Generate cycle_values starting from new_state
            cycle_values = []
            state_in_cycle = new_state
            for _ in range(cycle_length):
                a_cycle, b_cycle, c_cycle = state_in_cycle
                val = (a_cycle + b_cycle + c_cycle) % 10
                cycle_values.append(val)
                state_in_cycle = (b_cycle, c_cycle, val)
            # Calculate the position within the cycle
            start = cycle_start + 1
            remaining = K - start
            remainder = remaining % cycle_length
            print(cycle_values[remainder])
            found_cycle = True
            break
        else:
            prev_states[new_state] = step
            current_state = new_state

    if not found_cycle:
        print(current_state[2])