#include<bits/stdc++.h>
#define rep(i,a,b) for(int i=int(a);i<int(b);++i)
using namespace std;
typedef long long ll;
int INF = (1LL << 30) - 1;
int MOD = 1e9+7;
main(){
    int N,M;
    cin >> N >> M;
    string S,T;
    cin >> S >> T;
    int A[2] = {}, B[2] = {};
    for(auto c:S){
        if(c == 'A')A[0]++;
        else    B[0]++;
    }
    for(auto c:T){
        if(c == 'A')A[1]++;
        else    B[1]++;
    }
    cout << min(A[0], A[1]) + min(B[0], B[1]) << endl;
}