#include <stdio.h>

int min(int A, int B){return (A<B)?A:B;}
int main(){
	int N,M;
	char S[10001];
	int cntSA = 0, cntSB = 0;
	int cntTA = 0, cntTB = 0;

	scanf("%d %d",&N,&M);
	scanf("%s",S);
	for(int i = 0; i < N; i++){
		if(S[i] == 'A') cntSA++;
		else cntSB++;
	}
	scanf("%s",S);
	for(int i = 0; i < M; i++){
		if(S[i] == 'A') cntTA++;
		else cntTB++;
	}
	printf("%d\n",min(cntSA,cntTA)+min(cntSB,cntTB));

}