#include <bits/stdc++.h>
using namespace std;
int cnt[1000001];
int n, k;
int a[1000001];
int mod[1000001];
int main() {
  ios_base::sync_with_stdio(false);
  cin >> n >> k;
  for (int i = 1; i <= n; ++i) cin >> a[i];
  sort(a + 1, a + n + 1);
  for (int i = 1; i <= n; ++i) {
    for (int j = i + 1; j <= n; ++j) {
      ++cnt[a[j] - a[i]];
    }
  }
  int res = 1;
  for (;; ++res) {
    int cur = 0;
    for (int i = res; i <= 1000000; i += res) cur += cnt[i];
    if (cur > (k * (k + 1)) / 2) continue;
    cur = 0;
    for (int i = 1; i <= n; ++i) {
      if (mod[a[i] % res]) ++cur;
      ++mod[a[i] % res];
    }
    if (cur <= k) {
      cout << res;
      return 0;
    }
    memset(mod, 0, sizeof mod);
  }
}
