from itertools import combinations
def judge(s):
    for i in range(Kr,len(s)-Kr):
        if s[i] == s[i+Kr] == "R": return False
        if s[i] == s[i-Kr] == "R": return False
    for i in range(Kb,len(s)-Kb):
        if s[i] == s[i+Kb] == "B": return False
        if s[i] == s[i-Kb] == "B": return False
    return True

Kr,Kb = map(int,raw_input().split())
S = list(raw_input())
r = [i for i in range(30) if S[i] == "R"]
b = [i for i in range(30) if S[i] == "B"]
ans = 0
for i in range(10):
    if 30-i <= ans: break
    for j in range(10):
        if 30-i-j <= ans: break
        s = [S[k] for k in range(30) if k not in (pull_r+pull_b for pull_r in combinations(r,i) for pull_b in combinations(b,j))]
        if judge(s): ans = max(ans, len(s))
print ans