from collections import Counter

class Polymer:
    def __init__(self, data, remove=None):
        self.units = list(filter(lambda u: u.lower() != remove, data))
        self.index = 0

    def __len__(self):
        return len(self.units)

    def test(self, i):
        try:
            a, b = self.units[i], self.units[i + 1]
        except IndexError:
            return False
        if a != b and a.lower() == b.lower():
            return True
        return False

    def react(self):
        while self.test(self.index):
            del self.units[self.index:self.index + 2]
            if self.index > 0:
                self.index -= 1

    def process(self):
        while self.index < len(self) - 1:
            self.react()
            self.index += 1



with open('data/05.txt') as f:
    data = f.read().strip()


results = []
for unit_type in set(data.lower()):
    p = Polymer(data, remove=unit_type)
    p.process()
    results.append(len(p))

print(min(results))