import sys

input = sys.stdin.readline


def main():
    Kr, Kb = map(int, input().split())
    s = input()
    ans = 10
    for rm in range(1024):
        for bm in range(1024):
            ns = ''
            rc, bc = 0, 0
            for i in s:
                if i == 'R':
                    if (1 << rc) & rm:
                        ns += 'R'
                        if len(ns) > Kr and ns[-Kr-1] == 'R':
                            break
                    rc += 1
                elif i == 'B':
                    if (1 << bc) & bm:
                        ns += 'B'
                        if len(ns) > Kb and ns[-Kb-1] == 'B':
                            break
                    bc += 1
                else:
                    ns += 'W'
            else:
                ans = max(ans, len(ns))

    print(ans)


if __name__ == '__main__':
    main()