n,m=map(int,input().split())
s=list(map(lambda x:x,input()))
t=list(map(lambda x:x,input()))
p={}
q={}
for i in s:
    p[i]=p[i]+1 if i in p.keys() else 1
for i in t:
    q[i]=q[i]+1 if i in q.keys() else 1
ans=min(p['A'],q['A'])+min(p['B'],q['B'])
print(ans)