import sys
read=sys.stdin.buffer.read
readline=sys.stdin.readline
readlines=sys.stdin.buffer.readlines

kr, kb=map(int, readline().split())
s=readline().rstrip()
ans=0
for i in range(1<<20):
    t=""
    cnt=0
    for j in range(30):
        if s[j]=='R':
            if (i&(1<<cnt))==0:
                t+='R'
            cnt+=1
        elif s[j]=='B':
            if (i&(1<<cnt))==0:
                t+='B'
            cnt+=1
        else:
            t+='W'
    if len(t)<ans:
        continue
    dame=False
    for j, c in enumerate(t):
        if c=='R' and j+kr<len(t) and t[j+kr]=='R':
            dame=True
            break
        elif c=='B' and j+kb<len(t) and t[j+kb]=='B':
            dame=True
            break
    if not dame:
        ans=len(t)
print(ans)