import sys, math
sys.set_int_max_str_digits(0)

N, M = map(int, input().split())
S = input()
T = input()
cntA_S = S.count('A')
cntB_S = N - cntA_S
cntA_T = T.count('A')
cntB_T = M - cntA_T

ans = min(cntA_S, cntA_T) + min(cntB_S, cntB_T)
print(ans)