#include <bits/stdc++.h>
using namespace std;
#ifdef LOCAL
  #include "settings/debug.cpp"
#else
  #define Debug(...) void(0)
#endif
#define rep(i, n) for (int i = 0; i < (n); ++i)
using ll = long long;
using ull = unsigned long long;

int main() {
  int n, m;
  string s, t;
  cin >> n >> m >> s >> t;
  int a1 = 0, a2 = 0, b1 = 0, b2 = 0;
  for (char c : s) (c == 'A' ? a1 : a2)++;
  for (char c : t) (c == 'A' ? b1 : b2)++;
  cout << min(a1, b1) + min(a2, b2) << endl;
  return 0;
}