# coding:UTF-8
import sys
from itertools import combinations

MOD = 10 ** 9 + 7
INF = float('inf')

# 前処理なし
def comb(n, k):
    if n < k:
        return 0
    elif n < 0 or k < 0:
        return 0
    a = 1
    for i in range(k):
        a = a * (n - i)
    b = 1
    for i in range(1, k+1):
        b = b * i
    return a // b

Kr, Kb = list(map(int, input().split()))     # スペース区切り連続数字
S = input()     # 文字列

BRs = []
for i in range(30):
    if S[i] != "W":
        BRs.append(i)

for i in range(21):
    possible_i = False
    Nt = 30 - i

    for r in combinations(BRs, i):
        nums = set(r)
        Stmp = []
        for j in range(30):
            if j not in nums:
                Stmp.append(S[j])

        possible = True
        for j in range(Nt):
            if Stmp[j] == "W":
                continue

            elif Stmp[j] == "R":
                if j - Kr >= 0:
                    if Stmp[j - Kr] == "R":
                        possible = False
                        break
                if j + Kr <= Nt - 1:
                    if Stmp[j + Kr] == "R":
                        possible = False
                        break

            elif Stmp[j] == "B":
                if j - Kb >= 0:
                    if Stmp[j - Kb] == "B":
                        possible = False
                        break
                if j + Kb <= Nt - 1:
                    if Stmp[j + Kb] == "B":
                        possible = False
                        break

        if possible:
            possible_i = True
            break

    if possible_i:
        res = Nt
        break

print("{}".format(res))