def min(a, b):
    return a if a <= b else b

input_list = list(map(int,input().split()))
n, m = input_list
s = input()
t = input()

mudi = min(s.count('A'), t.count('A'))
gara = min(s.count('B'), t.count('B'))
res = mudi + gara

print(res)