#include <iostream>
using namespace std;
int main(){
    int n,m,a,b,mina,minb;
    string top,btm;
    cin>>n>>m>>top>>btm;
    
    mina = 0;minb = 0;
    for(int i=0;i<top.size();i++){
        if(top[i]=='A'){
            mina++;
        }else{
            minb++;
        }
    }
    
    a = 0;b = 0;
    for(int i=0;i<btm.size();i++){
        if(btm[i]=='A'){
            a++;
        }else{
            b++;
        }
    }
    
    if(a<mina)mina=a;
    if(b<minb)minb=b;
    cout<<mina+minb<<endl;
}