//Normal

#define _GLIBCXX_DEBUG
#define ll long long
#include <bits/stdc++.h>
using namespace std;
using Graph = vector<vector<int>>;

void print(auto a){
  cout << a;
}

void prints(auto a){
  cout << a << " ";
}

void prints(){
  cout << " ";
}

void printl(auto a){
  cout << a << endl;
}

void printl(){
  cout << endl;
}

void fix(int n){
  cout << fixed << setprecision(n);
}

int main(){
  int N, M; cin >> N >> M;
  string S, T; cin >> S >> T;
  int na = 0, nb = 0, ma = 0, mb = 0;
  for(int i = 0; i < N; i++) S[i] == 'A' ? na++ : nb++;
  for(int i = 0; i < M; i++) T[i] == 'A' ? ma++ : mb++;

  printl(min(na, ma) + min(nb, mb));

  return 0;
}