#include <iostream>
#include <algorithm>
#include <vector>
#include <set>
#include <map>
#include <queue>
#include <stack>
#include <cstdio>
#include <cstring>
#include <math.h>
using namespace std;
typedef long long ll;
typedef double D;
typedef pair<int,int> P;
#define M 1000000007
#define F first
#define S second
#define PB push_back
int n,m,a,b,c,d;
int main(void){
    cin>>n>>m;
    for(int i=0;i<n;i++){
        char s;
        scanf(" %c",&s);
        if(s=='A')a++;
        else b++;
    }
    for(int i=0;i<m;i++){
        char s;
        scanf(" %c",&s);
        if(s=='A')c++;
        else d++;
    }
    cout<<min(a,c)+min(b,d)<<endl;
}