#include <algorithm>
#include <array>
#include <cmath>
#include <cstdio>
#include <deque>
#include <iomanip>
#include <iostream>
#include <numeric>
#include <optional>
#include <queue>
#include <set>
#include <sstream>
#include <unordered_map>
#include <unordered_set>
#include <vector>

using namespace std;

int main() {
    int32_t n, m;
    string s, t;
    cin >> n >> m >> s >> t;
    int32_t sa = 0, sb = 0;
    for (auto c : s) {
        if (c == 'A')
            ++sa;
        else
            ++sb;
    }
    int32_t ta = 0, tb = 0;
    for (auto c : t) {
        if (c == 'A')
            ++ta;
        else
            ++tb;
    }
    cout << min(sa, ta) + min(sb, tb) << endl;
    return 0;
}