#include <iostream>
#include <set>
#include <vector>
#include <string>
#include <algorithm>
#include <iterator>

using namespace std;

#define rep(i, n) for(int i = 0; i < n; i++)
#define repi(i, n) for(auto i = (n).begin(); i != (n).end(); i++)
#define in_arr(type, a, n) copy_n(istream_iterator<type>(cin), n, (a).begin());
#define ll long long int

int main(){
    int n, m;
    string s, t;
    cin >> n >> m >> s >> t;
    int sa = 0, sb = 0, ta = 0, tb = 0;
    repi(i, s){
        if((*i) == 'A'){
            ++sa;
        }else{
            ++sb;
        }
    }
    repi(i, t){
        if((*i) == 'A'){
            ++ta;
        }else{
            ++tb;
        }
    }
    cout << min(sa, ta) + min(sb, tb) << endl;
    return 0;
}