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

char S[ 10010 ];
char T[ 10010 ];

int main()
{
int i;
int N;
int M;

	ios::sync_with_stdio( false );
	cin.tie( 0 );

	cin >> N;
	cin >> M;
	cin >> S;
	cin >> T;

	i = min( count( S, S + N, 'A' ), count( T, T + M, 'A' ) );
	i += min( count( S, S + N, 'B' ), count( T, T + M, 'B' ) );

	cout << i << endl;

	return 0;
}