with open("input") as f:
    data = f.read()

blocks = []
for idx, count in enumerate(data):
    block_char = "." if idx % 2 == 1 else str(idx // 2)
    for ii in range(int(count)):
        blocks.append(block_char)

empty_seek_idx = 0
last_non_empty_idx = len(blocks) - 1
while empty_seek_idx < last_non_empty_idx:
    if not blocks[empty_seek_idx] == ".":
        empty_seek_idx += 1
        continue

    if blocks[last_non_empty_idx] == ".":
        last_non_empty_idx -= 1
        continue

    blocks[empty_seek_idx], blocks[last_non_empty_idx] = blocks[last_non_empty_idx], blocks[empty_seek_idx]


def calculate_checksum(blocks: list[str]):
    checksum = 0
    for index, elem in enumerate(blocks):
        if elem == ".":
            break

        checksum += index * int(elem)

    return checksum


print(calculate_checksum(blocks))