import math
import sys
def S(): return sys.stdin.readline().rstrip()
def I(): return int(sys.stdin.readline().rstrip())
def MI(): return map(int, sys.stdin.readline().rstrip().split())
def LI(): return list(map(int, sys.stdin.readline().rstrip().split()))
def LS(): return list(sys.stdin.readline().rstrip().split())

n, m = MI()
s = S()
t = S()

ua = s.count('A')
ub = s.count('B')
da = t.count('A')
db = t.count('B')

ans = min(ua, da) + min(ub, db)
print(ans)