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import sys
from itertools import combinations
import pprint

subsequences = {}

def calculate_subsequences(word):
    indexes = [i for i in range(len(word))]
    for length in range(1, len(indexes)+1):
        for seq in combinations(indexes, length):
            substr = ''.join(word[i] for i in seq)
            if substr not in subsequences:
                subsequences[substr] = set([seq])
            else:
                subsequences[substr].add(seq)

def count_subsequences():
    count = 0
    for sub in subsequences.values():
        count += len(sub) > 1

    return count

def swap_letter(word, position, letter):
    affected = []
    for substr, seqs in subsequences.items():
        affected.extend(seq for seq in seqs if position in seq)
        subsequences[substr] = set(seq for seq in seqs if position not in seq)

    for sequence in affected:
        substr = ''.join(word[i] for i in sequence)
        if substr not in subsequences:
            subsequences[substr] = set([sequence])
        else:
            subsequences[substr].add(sequence)


if __name__ == "__main__":
    data = tuple(x for x in sys.stdin.read().split())
    length = int(data[0])
    operations = int(data[1])
    word = data[2]

    calculate_subsequences(word)
    print(count_subsequences())

    for q in range(operations):
        position = int(data[3+q*2])-1
        letter = data[3+q*2+1]
        if letter == word[position]:
            print(count_subsequences())
            continue

        word = word[:position] + letter + word[position+1:]
        swap_letter(word, position, letter)
        print(count_subsequences())