#include <bits/stdc++.h>
using namespace std;
int n, m;
int x[112345];
//检验间隔为 len 能不能凑出来 m 个牛舍
bool check(int len)
{
    int cnt = 1;
    int lastPos = x[1];
    for (int i = 2; i <= n; i++)
        if (x[i] - lastPos >= len)
        {
            cnt++;
            lastPos = x[i];
        }
    return cnt >= m;
}
int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    cin >> n >> m;
    for (int i = 1; i <= n; i++)
        cin >> x[i];
    sort(x + 1, x + n + 1);
    int l = 1;
    int r = x[n] - x[1];
    int ans = -1;
    while (l <= r)
    {
        int mid = (l + r) / 2;
        if (check(mid))
        {
            ans = mid;
            l = mid + 1;
        }
        else
            r = mid - 1;
    }
    cout << ans << "\n";
    return 0;
}