def dfs(i,num):
    global ans
    if i==L:
        ans = max(ans,num)
        return
    if ans >= num+L-i: return
    if s[i]=="W":
        dfs(i+1,num+1)
    elif s[i]=="R" and num-r not in R:
        R.append(num)
        dfs(i+1,num+1)
        R.pop()
    elif s[i]=="B" and num-b not in B:
        B.append(num)
        dfs(i+1,num+1)
        B.pop()
    if s[i] != "W":
        dfs(i+1,num)

r,b = map(int,readline().split())
s = input()
L = 30
ans = 12
R = []
B = []
dfs(0,0)
print(ans)