#! usr/bin/env python
# -*- coding: utf-8 -*-


def main():
    n, m = map(int, input().split())
    s, t = input(), input()

    s_a, s_b = 0, 0
    for i in range(n):
        if s[i] == "A":
            s_a += 1
        else:
            s_b += 1

    t_a, t_b = 0, 0
    for i in range(m):
        if t[i] == "A":
            t_a += 1
        else:
            t_b += 1

    print(min(s_a, t_a)+min(s_b, t_b))


if __name__ == '__main__':
    main()