using System;
using static System.Console;
using static System.Math;

public class Hello{
    public static void Main(){
        string[] input = ReadLine().Split(' ');
        int top = int.Parse(input[0]);
        int pan = int.Parse(input[1]);
        int mujit = 0;
        int mujip = 0;
        int garat = 0;
        int garap = 0;
        string ue = ReadLine();
        string st = ReadLine();
        for(int i=0;i<top;i++){
            if(ue[i] == 'A'){
                mujit++;
            }
        }
        for(int i=0;i<pan;i++){
            if(st[i] == 'A'){
                mujip++;
            }
        }
        garat = top-mujit;
        garap = pan-mujip;
        
        int a = Min(mujit,mujip);
        int b = Min(garat,garap);
        WriteLine(a+b);
    }
}