#include <iostream>
using namespace std;
int main(void){
    // Your code here!
    int N,M,OA=0,OB=0,UA=0,UB=0;
    scanf("%d %d",&N,&M);
    char O[N],U[M];
    for (int i=0;i<=N;i++){
        scanf("%c",&O[i]);
        if (O[i]=='A') OA+=1;
        if (O[i]=='B') OB+=1;
    }
    for (int i=0;i<=M;i++){
        scanf("%c",&U[i]);
        if (U[i]=='A') UA+=1;
        if (U[i]=='B') UB+=1;
    }
    printf("%d\n",(min(OA,UA)+min(OB,UB)));

}