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

N,M = map(int,readline().split())
S,T = read().split()

sa = S.count(b'A')
sb = N - sa
ta = T.count(b'A')
tb = M - ta

answer = min(sa,ta) + min(sb,tb)

print(answer)