#include <bits/stdc++.h>

using namespace std;
typedef long long ll;
#define REP(i,n) for(int i=0; i<int(n); i++)
#define FOR(i,m,n) for(int i=int(m); i<int(n); i++)
#define ALL(obj) (obj).begin(),(obj).end()
#define VI vector<int>
#define VLL vector<long long>
#define VVI vector<vector<int>>
#define VVLL vector<vector<long long>>
#define VC vector<char>
#define VS vector<string>
#define VVC vector<vector<char>>
#define fore(i,a) for(auto &i:a)

typedef pair <int, int> P;
template<class T> bool chmax(T &a, T b) { if (a < b) { a = b; return true; } return false; }
template<class T> bool chmin(T &a, T b) { if (a > b) { a = b; return true; } return false; }
const int  INF = 2147483647;
const ll INFL = 9223372036854775807;
const ll mod = 1000000007;





int main() {
	
	int n, m;
	cin >> n >> m;

	int a, b, c, d;
	a = b = c = d = 0;

	string s, t;
	cin >> s >> t;
	REP(i, s.size()) {
		if (s[i] == 'A')a++;
		else b++;
	}
	REP(i, t.size()) {
		if (t[i] == 'A')c++;
		else d++;
	}

	cout << min(a, c) + min(b, d) << endl;



	return 0;
}