#include <iostream>
#include <cstdio>
#include <algorithm>
#include <string>
#include <cstring>
#include <cctype>
#include <cmath>
#include <stack>
#include <queue>
#include <vector>
#include <set>
#include <map>
#include <list>
#include <stdio.h>
#include <string.h>
#include <cstdlib>
#include <math.h>
#include <bitset>
#include <iterator>
#include <iomanip>
#include <sstream>
#include <numeric>
#define INF 2000000000
using namespace std;
int dx[4]={1,0,-1,0},dy[4]={0,1,0,-1};
int gcd(int a,int b){if(a%b==0){return b;}else return gcd(b,a%b);}
int lcm(int a,int b){if(a==0){return b;} return a/gcd(a,b)*b;}
int MOD; template<class T> void mod(T &n){MOD=n;}
#define sym cout<<"---------"<<endl;
#define ll long long
#define PL pair<long long, long long>
#define P pair<int,int>
#define mk make_pair
#define en endl
#define WHITE 1
#define BLACK 2
#define GRAY 1
#define RE return 0
#define int ll


signed main(){
  int n,m;
  cin>>n>>m;
  int up_muji=0,up_e=0;
  int down_muji=0,down_e=0;
  for(int i=0; i<n; i++){
    char ch; cin>>ch;
    if(ch=='A') up_muji++;
    else up_e++;
  }
  for(int i=0; i<m; i++){
    char ch; cin>>ch;
    if(ch=='A') down_muji++;
    else down_e++;
  }
  int ans=min(up_e,down_e)+min(up_muji,down_muji);
  cout<<ans<<en;
}