#include <algorithm>
#include <cstdio>
#include <iostream>
#include <map>
#include <cmath>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>
#include <stdlib.h>
#include <stdio.h>
#include <bitset>
#include <cstring>
#include <deque>
#include <iomanip>
#include <limits>
#include <fstream>
using namespace std;
#define FOR(I,A,B) for(int I = (A); I < (B); ++I)
#define CLR(mat) memset(mat, 0, sizeof(mat))
typedef long long ll;

int main()
{
  ios::sync_with_stdio(false);
  cin.tie(0);
  int N, M;
  cin >> N >> M;
  string s, t;
  cin >> s >> t;
  int sa = 0, sb = 0;
  int ta = 0, tb = 0;
  FOR(i,0,N){
    s[i] == 'A' ? sa++ : sb++;
  }
  FOR(i,0,M){
    t[i] == 'A' ? ta++ : tb++;
  }
  cout << min(sa, ta) + min(sb, tb) << endl;
}