//Слава Україні, Героям слава

#include <bits/stdc++.h>

using namespace std;

struct SuffixArray {
    vector<int> sa, lcp_v;
    vector<vector<int>> cs;
    int n;

    int add(int a, int b) { return a + b >= n ? a + b - n : a + b; }
    int sub(int a, int b) { return a - b < 0 ? a - b + n : a - b; }

    SuffixArray(string& s, bool store_steps = false, bool build_lcp = true) {
        s += ' ';
        n = (int)s.size();
        sa = sort_shifts(s, store_steps);
        if (build_lcp) {
            lcp_v = build_lcp_v(s);
            lcp_v.erase(lcp_v.begin());
        }
        sa.erase(sa.begin());
        s.pop_back();
    }

    vector<int> sort_shifts(string& s, bool store_steps) {
        const int ALPHA_SIZE = 256;
        vector<int> p(n), c(n), cnt(ALPHA_SIZE);
        for (char ch : s) cnt[(int)ch]++;
        for (int i = 1; i < ALPHA_SIZE; i++) cnt[i] += cnt[i - 1];

        for (int i = 0; i < n; i++) {
            cnt[s[i]]--;
            p[cnt[s[i]]] = i;
        }

        for (int i = 1; i < n; i++)
            c[p[i]] = c[p[i - 1]] + (s[p[i]] != s[p[i - 1]]);

        if (store_steps) cs.push_back(c);

        vector<int> cn(n), pn(n);

        for (int k = 0; (1 << k) < n; k++) {
            int nclass = c[p[n - 1]] + 1;
            cnt.assign(nclass, 0);

            for (int i = 0; i < n; i++) {
                pn[i] = sub(p[i], (1 << k));
                cnt[c[i]]++;
            }

            for (int i = 1; i < nclass; i++)
                cnt[i] += cnt[i - 1];

            for (int i = n - 1; i >= 0; i--) {
                cnt[c[pn[i]]]--;
                p[cnt[c[pn[i]]]] = pn[i];
            }

            cn[p[0]] = 0;
            for (int i = 1; i < n; i++) {
                pair<int, int> a = { c[p[i]], c[add(p[i], (1 << k))] };
                pair<int, int> b = { c[p[i - 1]], c[add(p[i - 1], (1 << k))] };
                cn[p[i]] = cn[p[i - 1]] + (a != b);
            }

            swap(c, cn);
            if (store_steps) cs.push_back(c);

        }

        return p;
    }

    vector<int> build_lcp_v(string& s) {
        vector<int> ans(n - 1), rank(n);
        for (int i = 0; i < n; i++) rank[sa[i]] = i;

        for (int i = 0, k = 0; i < n - 1; i++) {
            if (rank[i] == n - 1) continue;
            int j = sa[rank[i] + 1];
            while (s[i + k] == s[j + k]) k++;
            ans[rank[i]] = k;
            if (k) k--;
        }

        return ans;
    }

    int lcp(int i, int j) {
        if (i == j) return n - i - 1;
        int ans = 0;
        for (int k = (int)cs.size() - 1; k >= 0; k--) {
            if (cs[k][i] == cs[k][j]) {
                int val = (1 << k);
                ans += val, i += val, j += val;
            }
        }
        return ans;
    }

    long long diff_substr() {
        int sz = n - 1;
        long long ans = sz - sa[0];
        for (int i = 1; i < (int)sa.size(); i++) ans += sz - sa[i] - lcp_v[i - 1];
        return ans;
    }

    long long diff_substr_sz_sum() {
        int sz = n - 1;
        auto sum = [](int l, int r) { return (1ll * (l + r) * (r - l + 1)) / 2; };
        long long ans = sum(1, sz - sa[0]);
        for (int i = 1; i < (int)sa.size(); i++) ans += sum(lcp_v[i - 1] + 1, sz - sa[i]);
        return ans;
    }

};

const int N = 1e6 + 7;

int par[N], sz[N];

int find(int a) {
    return a == par[a] ? a : par[a] = find(par[a]);
}

void unite(int a, int b) {
    if((a = find(a)) == (b = find(b))) return;
    if(sz[b] > sz[a]) swap(a, b);
    sz[a] += sz[b];
    par[b] = a;
}

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    for(int i = 0; i < N; i++) {
        par[i] = i;
        sz[i] = 1;
    }
    long long n, k;
    cin >> n >> k;
    string s;
    cin >> s;
    SuffixArray sa(s);
    vector<vector<pair<int, int>>> q(n + 1);
    vector<int> invsa(n);
    for(int i = 0; i < (int)sa.lcp_v.size(); i++) {
        q[sa.lcp_v[i]].emplace_back(sa.sa[i], sa.sa[i + 1]);
    }
    for(int i = 0; i < n; i++) {
        invsa[sa.sa[i]] = i;
    }
    vector<pair<int, int>> ans;
    for(long long i = n; i; i--) {
        for(auto [a, b] : q[i]) {
            unite(a, b);
        }
        for(auto [a, b] : q[i]) {
            if(i * sz[find(a)] == k) {
                ans.emplace_back(find(a), i);
            }
        }
    }
    // i forgot to add the ones of length k that have nothing in common lol
    for(int i = 1; i < n - 1; i++) {
        if(sa.lcp_v[i - 1] < k and sa.lcp_v[i] < k) {
            if(n - sa.sa[i] >= k) {
                ans.emplace_back(sa.sa[i], k);
            }
        }
    }
    if(sa.lcp_v[0] < k and n - sa.sa[0] >= k) {
        ans.emplace_back(sa.sa[0], k);
    }
    if(sa.lcp_v[n - 2] < k and n - sa.sa[n - 1] >= k) {
        ans.emplace_back(sa.sa[n - 1], k);
    }
    sort(ans.begin(), ans.end(), [&](pair<int, int> a, pair<int, int> b) {
        if(invsa[a.first] == invsa[b.first]) {
            return a.second < b.second;
        }
        return invsa[a.first] < invsa[b.first];
    });
    ans.erase(unique(ans.begin(), ans.end()), ans.end());
    cout << ans.size() << "\n";
    if(ans.size()) {
        cout << s.substr(ans[0].first, ans[0].second) << "\n";
        cout << s.substr(ans.back().first, ans.back().second) << "\n";
    }
    return 0;
}