#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using Graph = vector<vector<int>>;
int main() {
  int N,M; cin >> N >> M;
  string A; cin >> A;
  string B; cin >> B;
  int ua = 0;
  int ub = 0;
  int da = 0;
  int db = 0;
  for(int i = 0; i < N; i++) {
    if(A[i] == 'A') {
      ua++;
    }
    if(A[i] == 'B') {
      ub++;
    }
  }
  for(int i = 0; i < M; i++) {
    if(B[i] == 'A') {
      da++;
    }
    if(B[i] == 'B') {
      db++;
    }
  }
  int ans = min(ua,da) + min(ub,db);
  cout << ans << endl;
}