Kr, Kb = map(int, input().split())
S = list(input())
M = 1 << 10
ans = 0

def check(A):
    for i in range(len(A)):
        if A[i] == 0:
            if i - Kr >= 0:
                if A[i - Kr] == 0:
                    return False
            if i + Kr <= len(A) - 1:
                if A[i + Kr] == 0:
                    return False
        if A[i] == 1:
            if i - Kb >= 0:
                if A[i - Kb] == 1:
                    return False
            if i + Kb <= len(A) - 1:
                if A[i + Kb] == 1:
                    return False
    return True


for sr in range(M):
    for sb in range(M):
        ir, ib = 0, 0
        temp = []
        for i in range(30):
            if S[i] == "R":
                if (sr >> ir) & 1:
                    temp.append(0)
                ir += 1
            elif S[i] == "B":
                if (sb >> ib) & 1:
                    temp.append(1)
                ib += 1
            else:
                temp.append(2)
        if check(temp):
            ans = max(ans, len(temp))

print(ans)