n,m = map(int,input().split())
s = input().strip()
t = input().strip()
a_s = a_t = 0
b_s = b_t = 0

bnum= []
for i in range(n) :
    if s[i] == 'A' :
        a_s += 1
    else :
        b_s += 1
for i in range(m) :
    if t[i] == 'A' :
        a_t += 1
    else :
        b_t += 1
print(min(a_s,a_t) + min(b_s,b_t) )