# import sys; input = sys.stdin.buffer.readline
# sys.setrecursionlimit(10**7)
from collections import defaultdict
con = 10 ** 9 + 7; INF = float("inf")

def getlist():
	return list(map(int, input().split()))

#処理内容
def main():
	N, M = getlist()
	S = input()
	T = input()
	Sa = 0; Sb = 0
	Ta = 0; Tb = 0
	for i in S:
		if i == "A":
			Sa += 1
		else:
			Sb += 1

	for i in T:
		if i == "A":
			Ta += 1
		else:
			Tb += 1

	ans = min(Sa, Ta) + min(Sb, Tb)
	print(ans)



if __name__ == '__main__':
	main()