r, b = map(int, input().split())
S = input()

ans = 0
for bit in range(1 << 20):
    p = 0
    T = []
    m = 30
    for s in S:
        if s == "W":
            T.append(s)
        else:
            if bit >> p & 1:
                T.append(s)
            else:
                m -= 1
            p += 1
    if m < ans:
        continue
    ok = True
    for i, t in enumerate(T):
        if t == "R":
            if i + r < m and T[i + r] == "R":
                ok = False
                break
        elif t == "B":
            if i + b < m and T[i + b] == "B":
                ok = False
                break
    if ok:
        ans = m
print(ans)