#include <bits/stdc++.h>

using namespace std;
typedef long long ll;

int main() {
  int n, m;
  cin >> n >> m;

  string s, t;
  cin >> s >> t;

  int scnta = 0;
  int scntb = 0;
  for (int i = 0; i < n; ++i) {
    if (s[i] == 'A') scnta++;
    else scntb++;
  }

  int tcnta = 0;
  int tcntb = 0;
  for (int i = 0; i < m; ++i) {
    if (t[i] == 'A') tcnta++;
    else tcntb++;
  }
  int ans = min(scnta, tcnta) + min(scntb, tcntb);
  cout << ans << endl;
  return 0;
}