import sys
sys.setrecursionlimit(10000000)
MOD = 10 ** 9 + 7
INF = 10 ** 15

N,M = map(int,input().split())
S = input()
T = input()
a = S.count('A')
b = S.count('B')
c = T.count('A')
d = T.count('B')
ans = min(a,c) + min(b,d)
print(ans)