n,m=map(int,input().split())
s=input()
t=input()
sa=0
sb=0
ta=0
tb=0

for i in range(n):
  if s[i]=='A':
    sa+=1
  else:
    sb+=1
for i in range(m):
  if t[i]=='A':
    ta+=1
  else:
    tb+=1
print(min(sa,ta)+min(sb,tb))