window_size = 4
retained_positions = []

for position in range(10):
    retained_positions.append(position)

    if len(retained_positions) > window_size:
        retained_positions.pop(0)

    print(f"after token {position}: {retained_positions}")

print("maximum retained positions:", window_size)

# Output:
"""
after token 0: [0]
after token 1: [0, 1]
after token 2: [0, 1, 2]
after token 3: [0, 1, 2, 3]
after token 4: [1, 2, 3, 4]
after token 5: [2, 3, 4, 5]
after token 6: [3, 4, 5, 6]
after token 7: [4, 5, 6, 7]
after token 8: [5, 6, 7, 8]
after token 9: [6, 7, 8, 9]
maximum retained positions: 4
"""