#include <bits/stdc++.h>
using namespace std;

#define int long long

#define rep(i,s,n) for(int i = s;i<n;i++)
#define repe(i,s,n) for(int i = s;i<=n;i++)
#define rrep(i,s,n) for(int i = (n)-1;i>=(s);i--)
#define all(v) (v).begin(),(v).end()
#define pb push_back
#define fi first
#define se second
#define chmin(a,b) a=min((a),(b))
#define chmax(a,b) a=max((a),(b))
typedef long long ll;
typedef pair<int,int>pint;
typedef vector<int>vint;
typedef vector<pint>vpint;
typedef pair<pint,int> P1;
typedef pair<int,pint> P2;
typedef pair<pint,pint> PP;
static const ll maxLL = (ll)1 << 62;
const ll MOD=1000000007;
const ll INF=1e18;

int N,M;
string s,t;
int cnt1=0,cnt2=0;

signed main() {
    cin>>N>>M;
    cin>>s>>t;
    rep(i,0,N){
        if(s[i]=='A')cnt1++;
    }
    rep(i,0,M){
        if(t[i]=='A')cnt2++;
    }
    cout<<min(cnt1,cnt2)+min(N-cnt1,M-cnt2)<<endl;
    return 0;
}