r, b = map(int, input().split())
rgw = input()

d = list(rgw)

i = 0
while(1):
    if i >= len(d):
        break
    if d[i] == 'R':
        while(len(d)>  i + r and d[i + r] == 'R'):
            del(d[i + r])
    if d[i] == 'B':
        while(len(d)> i + b and d[i + b] == 'B'):
            del(d[i + b])
    i += 1
print(len(d))