n, m = map(int, input().split())
na, nb = 0, 0
ma, mb = 0, 0
s = input()
t = input()
for i in range(len(s)):
    if s[i] == "A":
        na += 1
    else:
        nb += 1

for i in range(len(t)):
    if t[i] == "A":
        ma += 1
    else:
        mb += 1

print(min(na, ma) + min(nb, mb))