#include <bits/stdc++.h>
using namespace std;
int MAX = (int)1e6;
int cnt[5 + (int)1e6], a[5000], n, k, lastSeen[5 + (int)1e6];
int main() {
  scanf("%d%d", &n, &k);
  for (int i = 0; i < n; i++) scanf("%d", a + i);
  sort(a, a + n);
  for (int i = 0; i < n; i++)
    for (int j = i + 1; j < n; j++) cnt[a[j] - a[i]]++;
  for (int m = 1;; m++) {
    int num_of_pairs = 0;
    for (int j = m; j < MAX; j += m) {
      num_of_pairs += cnt[j];
    }
    if (num_of_pairs > k * (k + 1) / 2) {
      continue;
    }
    int num_to_remove = 0;
    for (int i = 0; i < n; i++) {
      int rem = a[i] % m;
      if (lastSeen[rem] == m) num_to_remove++;
      lastSeen[rem] = m;
    }
    if (num_to_remove <= k) {
      printf("%d\n", m);
      return 0;
    }
  }
}
