/* -*- coding: utf-8 -*-
 *
 * 717.cc: No.717 ファッションへのこだわり - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

/* typedef */

/* global variables */

/* subroutines */

/* main */

int main() {
  int n, m;
  string s, t;
  cin >> n >> m >> s >> t;

  int sa = 0, ta = 0;
  for (int i = 0; i < n; i++)
    if (s[i] == 'A') sa++;
  for (int i = 0; i < m; i++)
    if (t[i] == 'A') ta++;

  printf("%d\n", min(sa, ta) + min(n - sa, m - ta));
  return 0;
}