#include <bits/stdc++.h>
using namespace std;
typedef long long ll;

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