#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll = long long;
using ld = long double;

ll N, M;
string S, T;
map<char, ll> mpS, mpT;

int main() {
  cin >> N >> M;
  cin >> S >> T;
  for (int i = 0; i < N; i++) mpS[S[i]]++;
  for (int i = 0; i < M; i++) mpT[T[i]]++;
  cout << min(mpS['A'], mpT['A']) + min(mpS['B'], mpT['B']) << endl;
  return 0;
}