#include <algorithm>
#include <cassert>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <iomanip>
#include <iostream>
#include <map>
#include <memory>
#include <numeric>
#include <set>
#include <stack>
#include <string>
#include <vector>

#define rep(i,a,b) for(int i=(a);i<(b);++i)
#define MOD 1000000007
#define int long long
using ll = long long;
using namespace std;
const int INF = 1LL << 50;
using P = pair<int, int>;

template <class T>
bool chmin(T &a, T b) {
    if (a > b) {
        a = b;
        return true;
    }
    else {
        return false;
    }
}
template <class T>
bool chmax(T &a, T b) {
    if (a < b) {
        a = b;
        return true;
    }
    else {
        return false;
    }
}
struct Setup {
    Setup() {
        cin.tie(0);
        ios::sync_with_stdio(false);
        cout << fixed << setprecision(20);
    }
} SETUP;

signed main() {
    int n, m; cin >> n >> m;
    string s, t; cin >> s >> t;
    int cnt_s[2] = { 0 };
    int cnt_t[2] = { 0 };
    for (auto c : s) {
        cnt_s[c - 'A']++;
    }
    for (auto c : t) {
        cnt_t[c - 'A']++;
    }

    int ans = 0;
    rep(i, 0, 2) {
        ans += min(cnt_s[i], cnt_t[i]);
    }
    cout << ans << endl;
}