#include "bits/stdc++.h"
using namespace std;
#define fastcin {\
    cin.tie(0);\
    ios::sync_with_stdio(false);\
}
#define rep(i, a, b) for(int i = a; i < b; i++)
#define print(x) cout << x << "\n"

int main() {
    fastcin;
    int n, m;
    string s, t;
    cin >> n >> m >> s >> t;
    int ta = 0, tb = 0;
    rep(i, 0, n) {
        if(s[i]=='A') ta++;
        else tb++;
    }
    int ba = 0, bb = 0;
    rep(i, 0, m) {
        if(t[i]=='A') ba++;
        else bb++;
    }
    int ans = min(ta, ba) + min(ba, bb);
    print(ans);
    return 0;
}