#include <cstdio>
#include <cmath>
#include <vector>
#include <algorithm>
#include <cassert>
#include <cstring>
#include <climits>
#include <queue>
#include <ctime>
using namespace std;
typedef long long LL;

#ifdef INFOARENA
#define ProblemName "substr"
#endif

#define MCONCAT(A, B) A B
#ifdef ProblemName
#define InFile MCONCAT(ProblemName, ".in")
#define OuFile MCONCAT(ProblemName, ".out")
#else
#define InFile "fis.in"
#define OuFile "fis.out"
#endif

const int MAXN = 17000;
char buf[MAXN];
int N, M, K;
int h[2][MAXN];
const int modnum[2] = { 961748941, 982451653 };
int pw[2][MAXN];
const int B = 29;

void prec(int id) {
  pw[id][0] = 1;
  for (int i = 1; i <= N; ++i)
    pw[id][i] = (int)((1LL * pw[id][i - 1] * B) % modnum[id]);
  h[id][0] = buf[0] - 'a';
  for (int i = 1; i < N; ++i)
    h[id][i] = (int)((1LL * h[id][i - 1] * B + buf[i] - 'a') % modnum[id]);
}

int getHash(int id, int r, int L) {
  int l = r - L + 1;
  if (l <= 0)
    return h[id][r];
  int p = (int)((
    h[id][r] - (1LL * h[id][l - 1] * pw[id][L]) % modnum[id]
    ) % modnum[id]);
  if (p < 0) p += modnum[id];
  return p;
}

inline bool eqAt(int id, int i, int j) {
  return getHash(id, i, M) == getHash(id, j, M);
}

inline bool eqAt(int i, int j) {
  return eqAt(0, i, j) && eqAt(1, i, j);
}

int nrapp(int j) {
  int ans = 0;
  for (int i = M - 1; i < N; ++i)
  if (eqAt(i, j))
    ++ans;
  return ans;
}

bool canDo() {
  int best = 0;
  for (int j = M - 1; j < N; ++j) {
    int cand = nrapp(j);
    if (cand > best)
      best = cand;
  }
  return (best >= K);
}

int binSrch() {
  int left = 1, right = N;
  int found = 0;
  while (left <= right) {
    M = left + (right - left) / 2;
    if (canDo()) {
      found = M;
      left = M + 1;
    }
    else
      right = M - 1;
  }
  return found;
}

int main() {
  assert(freopen(InFile, "r", stdin));
  assert(freopen(OuFile, "w", stdout));
  scanf("%d%d", &N, &K);
  scanf("%s", buf);
  prec(0); prec(1);
  printf("%d\n", binSrch());
  return 0;
}