#include <bits/stdc++.h>
#include <iterator>
#include <tuple>
using namespace std;

int main()
{
  int n, m;
  cin >> n >> m;
  string s, t;
  cin >> s;
  cin >> t;
  int cnta[2] = {}, cntb[2] = {};
  for (int i = 0; i < n; ++i)
  {
    if (s[i] == 'A')
      cnta[0]++;
    if (s[i] == 'B')
      cntb[0]++;
  }
  for (int i = 0; i < m; ++i)
  {
    if (t[i] == 'A')
      cnta[1]++;
    if (t[i] == 'B')
      cntb[1]++;
  }
  cout << min(cnta[0], cnta[1]) + min(cntb[0], cntb[1]) << endl;

  return 0;
}