#!/usr/bin/env python3

with open('input.txt', 'r') as f:
    polymer = f.read()

print('Polymer length:', len(polymer))

modifications = True
rounds = 0
while modifications:
    modifications = False
    rounds += 1
    mods = 0
    
    new_polymer = []
    skip = False
    for i, el in enumerate(polymer[:-1]):
        if skip:
            skip = False
            continue
        next_el = polymer[i + 1]
        if el != next_el and el.upper() == next_el.upper():
            modifications = True
            mods += 1
            skip = True
            continue

        new_polymer.append(el[-1])

    if not skip:
        new_polymer.append(polymer[-1])

    polymer = ''.join(new_polymer)

    print(f'Round: {rounds}. Modifications found: {mods}. Polymer length: {len(polymer)}')

print(polymer)
print(len(polymer))