#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
#define F first
#define S second
#define pii pair<int, int>
#define eb emplace_back
#define all(v) v.begin(), v.end()
#define rep(i, n) for (int i = 0; i < n; ++i)
#define rep3(i, l, n) for (int i = l; i < n; ++i)
#define chmax(a, b) a = max(a, b)
#define chmin(a, b) a = min(a, b)
#define out(a) cout << a << endl
#define SZ(v) (int)v.size()
#define inf (int)(1e9+7)

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    int n, m;
    cin >> n >> m;
    string s, t;
    cin >> s >> t;
    int sa = 0, sb = 0;
    int ta = 0, tb = 0;
    rep(i, SZ(s)) if (s[i] == 'A') sa++; else sb++;
    rep(i, SZ(t)) if (t[i] == 'A') ta++; else tb++;
    out(min(sa, ta) + min(sb, tb));
}