from collections import defaultdict
import sys,heapq,bisect,math,itertools,string
sys.setrecursionlimit(10**8)
INF = float('inf')
mod = 10**9+7
AtoZ = [chr(i) for i in range(65,65+26)]
atoz = [chr(i) for i in range(97,97+26)]

min_val = INF

N,M = map(int,input().split())
S = list(input())
T = list(input())
Sa = S.count('A')
Sb = S.count('B')
Ta = T.count('A')
Tb = T.count('B')
print(min(Sa,Ta)+min(Sb,Tb))