n, m = map(int, input().split())
s = str(input())
t = str(input())
x = 0
y = 0
for i in range(n):
    if s[i] == 'A':
        x += 1
    else:
        y += 1

z = 0
w = 0
for i in range(m):
    if t[i] == 'A':
        z += 1
    else:
        w += 1

ans = min(x, z)+min(y, w)
print(ans)