code_circle_of_digit

/// solution : https://pastebin.com/JiDCvA5T
#include<bits/stdc++.h>
using namespace std;

typedef pair<int, int> ii;
typedef unsigned long long ULL;

const int N = 4e5 + 4, LOG = 20;
int n, k, Up, Down;
string S;

ULL Pow[N], Hash[N];

void Build_Hash() {
	for (int i = 0; i <= 2*n; ++i) Pow[i] = (i == 0) ? 1 : Pow[i-1] * 31LL;
	for (int i = 1; i <= 2*n; ++i) Hash[i] = Hash[i-1] * 31LL + S[i] - '0';
}
ULL getHash(int i, int j) { return Hash[j] - Hash[i-1] * Pow[j-i+1]; }

struct data {
	int l, r;
	data() {}; data(int l, int r) : l(l), r(r) {};

	bool operator < (const data &a) const {
		int low = 1, high = r-l+1, Equal = 0;
		while (low <= high) {
			int mid = (low + high) / 2;
			if (getHash(l, l+mid-1) == getHash(a.l, a.l+mid-1)) { Equal = mid; low = mid + 1; }
			else high = mid - 1;
		}
			// cerr << S[7] << " " << S[8] << '\n';
			// cerr << Equal << '\n';
			// cerr << "^^ " << l << " " << r << " " << a.l << " " << a.r << '\n';
			// cerr << "%% " << l+Equal-1 << " " << S[l+Equal-1] << '\n';
			// cerr << S[l+Equal] << " " << S[a.l+Equal] << '\n';
		if (Equal == r-l+1) return false;
		return S[l+Equal] < S[a.l+Equal];
	}
};

vector<data> V;
int par[N][LOG+4];

int Jump(int u, int step) {
	for (int i = LOG; i >= 0; --i)
		if (step - (1<<i) >= 0) u = par[u][i], step -= (1<<i);
	return (step == 0) ? u : -1;
}

bool check(int mid) {
	for (int i = 1; i <= 2*n; ++i) par[i][0] = -1;

	for (int i = 0; i <= mid; ++i) par[V[i].l][0] = V[i].r+1;
	for (int i = 1; i <= 2*n; ++i)
		if (par[i][0] == -1) par[i][0] = i + Down;

	for (int j = 1; j <= LOG; ++j) for (int i = 1; i <= 2*n; ++i)
		par[i][j] = par[par[i][j-1]][j-1];

	for (int i = 1; i <= 2*n; ++i) {
		int ver = Jump(i, k);
		if (ver - i >= n) return true;
	}
	return false;
}

void sol() {
	Build_Hash();

	if (n % k == 0) { Up = n/k; Down = n/k-1; }
	else { Up = n/k + 1; Down = n/k; }

	for (int i = 1; i <= 2*n; ++i)
		if (i + Up - 1 <= 2*n) V.push_back(data(i, i+Up-1));

	sort(V.begin(), V.end());

	int l = 0, r = (int) V.size(), res = -1;
	while (l <= r) {
		int mid = (l + r) / 2;
		if (check(mid)) { res = mid; r = mid - 1; }
		else l = mid + 1;
	}
	cout << S.substr(V[res].l, Up) << '\n';
}

int main() {
	ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
	if (fopen("input.txt", "r")) {
		freopen("input.txt", "r", stdin);
	}
	else if (fopen("B.in", "r")) {
		freopen("B.in", "r", stdin);
	}

	cin >> n >> k >> S;
	S = " " + S + S;

	sol();

	return 0;
}