#ifndef SorahISA
#define SorahISA
#include SorahISA __FILE__ SorahISA

const int maxc = 3'000'000; /// length <= 20

struct Trie {
    
    struct Node {
        array<int, 2> cnt;
        vector<pair<int, char>> ch;
        Node() : ch(0) { cnt[0] = cnt[1] = 0; }
        int& operator [] (char c) {
            for (int i = 0; i < SZ(ch); ++i) {
                if (ch[i].second == c) return ch[i].first;
            }
            ch.emplace_back(-1, c);
            return ch.back().first;
        }
    };
    
    vector<Node> trie;
    
    void init() {
        trie.clear(), trie.shrink_to_fit();
        trie.eb();
    }
    
    void insert(const string &S, int tp) {
        int now = 0;
        for (const char &c : S) {
            if (int &tmp = trie[now][c]; tmp == -1) tmp = SZ(trie), trie.eb(), now = tmp;
            else now = tmp;
        }
        ++trie[now].cnt[tp];
    }
    
    int64 dp(int now, int hei) {
        int64 ans = 0;
        for (auto [ch, c] : trie[now].ch) {
            if (ch != -1) {
                ans += dp(ch, hei-1);
                trie[now].cnt[0] += trie[ch].cnt[0];
                trie[now].cnt[1] += trie[ch].cnt[1];
            }
        }
        // debug(tmp, hei, trie[now].cnt[0], trie[now].cnt[1]);
        int64 score = min(trie[now].cnt[0], trie[now].cnt[1]);
        ans += score * hei;
        trie[now].cnt[0] -= score, trie[now].cnt[1] -= score;
        return ans;
    }
    
};

void solve() {
    int N, K; cin >> N >> K;
    string S, T; cin >> S >> T;
    
    Trie trie; trie.init();
    
    for (int i = 0; i <= N-K; ++i) trie.insert(S.substr(i, min(K, maxc/N)), 0);
    for (int i = 0; i <= N-K; ++i) trie.insert(T.substr(i, min(K, maxc/N)), 1);
    
    cout << trie.dp(0, K) << "\n";
}

int32_t main() {
    fastIO();
    
    int t = 1; // cin >> t;
    for (int _ = 1; _ <= t; ++_) {
        solve();
    }
    
    return 0;
}

#else

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

// #define int int64_t
#define double __float80
using int64 = long long;
using pii = pair<int, int>;
template <typename T> using Prior = std::priority_queue<T>;
template <typename T> using prior = std::priority_queue<T, vector<T>, greater<T>>;

#define eb emplace_back
#define ef emplace_front
#define ee emplace
#define pb pop_back
#define pf pop_front
#define ALL(x) begin(x), end(x)
#define RALL(x) rbegin(x), rend(x)
#define SZ(x) ((int)(x).size())

#ifdef local
#define fastIO() void()
#define debug(...) \
    fprintf(stderr, "%s", "\u001b[33m"), \
    fprintf(stderr, "At [%s], line %d: (%s) = ", __FUNCTION__, __LINE__, #__VA_ARGS__), \
    _do(__VA_ARGS__), \
    fprintf(stderr, "%s", "\u001b[0m")
template <typename T> void _do(T &&_t) {cerr << _t << "\n";}
template <typename T, typename ...U> void _do(T &&_t, U &&..._u) {cerr << _t << ", ", _do(_u...);}
#else
#define fastIO() ios_base::sync_with_stdio(0), cin.tie(0)
#define debug(...) void()
#endif

template <typename T, typename U> bool chmin(T &lhs, U rhs) {return lhs > rhs ? lhs = rhs, 1 : 0;}
template <typename T, typename U> bool chmax(T &lhs, U rhs) {return lhs < rhs ? lhs = rhs, 1 : 0;}

#endif