#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (n); ++i)
#define srep(i,s,t) for (int i = s; i < t; ++i)
#define drep(i,n) for(int i = (n)-1; i >= 0; --i)
using namespace std;
typedef long long int ll;
typedef pair<int,int> P;
#define yn {puts("Yes");}else{puts("No");}
#define MAX_N 200005

int main() {
    int n, m;
    cin >> n >> m;
    string s, t;
    cin >> s >> t;
    int a[2] = {};
    int b[2] = {};
    rep(i,n){
        if(s[i] == 'A')a[0]++;
        else b[0]++;
    }
    rep(i,m){
        if(t[i] == 'A')a[1]++;
        else b[1]++;
    }

    int ans = min(a[0],a[1]) + min(b[0],b[1]);

    cout << ans << endl;
    return 0;
}