def read_data():
    Kr, Kb = map(int, input().split())
    S = input()
    return Kr, Kb, S

def solve(Kr, Kb, S):
    if is_valid(S, Kr, Kb):
        return len(S)
    strings = set([S])
    for i in range(20):
        new_strings = set()
        for string in strings:
            for i, c in enumerate(string):
                if c == 'W':
                    continue
                new_string = string[:i] + string[i+1:]
                if new_string in new_strings:
                    continue
                if is_valid(new_string, Kr, Kb):
                    return len(new_string)
                new_strings.add(new_string)
        strings = new_strings

def is_valid(S, Kr, Kb):
    n = len(S)
    for i, c in enumerate(S):
        if c == 'B':
            if i >= Kb and S[i - Kb] == 'B':
                return False
            if i + Kb < n and S[i + Kb] == 'B':
                return False
        elif c == 'R':
            if i >= Kr and S[i - Kr] == 'R':
                return False
            if i + Kr < n and S[i + Kr] == 'R':
                return False
    return True

Kr, Kb, S = read_data()
print(solve(Kr, Kb, S))