#include <iostream>
#include <string>
using namespace std;
int main(int argc, char* argv[])
{
	int N,M,i;
	cin>>N>>M;
	string S1,S2;
	cin>>S1;
	cin>>S2;
	int S1_A=0;
	int S1_B=0;
	int S2_A=0;
	int S2_B=0;
	for (i=0;i<N;i++){
		if (S1[i]=='A'){
			S1_A++;
		}else{
			S1_B++;
		}
	}
	for (i=0;i<M;i++){
		if (S2[i]=='A'){
			S2_A++;
		}else{
			S2_B++;
		}
	}
	cout<<min(S1_A,S2_A)+min(S1_B,S2_B)<<endl;
	return 0;
}