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

int main()
{
	int N, M;
	string S, T;
	cin >> N >> M >> S >> T;

	int na = 0;
	for( int i = 0; i < N; i++ ) {
		if( S[i] == 'A' ) na++;
	}
	int ma = 0;
	for( int i = 0; i < M; i++ ) {
		if( T[i] == 'A' ) ma++;
	}
	int ans = min( na, ma ) + min( N - na, M - ma );

	cout << ans << endl;
}