#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define rep(i,n) for(int (i)=0;(i)<(n);(i)++)

int main() {
  ll n,m;cin>>n>>m;
  string s,t;cin>>s>>t;
  ll sa=0,sb=0,ta=0,tb=0;
  for(auto &ch : s) {
    if(ch=='A')sa++;
    if(ch=='B')sb++;
  }
  for(auto &ch : t) {
    if(ch=='A')ta++;
    if(ch=='B')tb++;
  }	
  cout<<min(sa,ta)+min(sb,tb)<<endl;
  return 0;
}