#include <iostream>
#include <algorithm>
#include <vector>

using namespace std;

bool verify(int T, int n, int m, vector<int> & v) {
    int projects = 0, nextStartDate = 0;

    for (int i = 0; i < n; i++) {
        if (v[i] >= nextStartDate) {
            projects++;
            nextStartDate = v[i] + T;
        }
    }

    return (projects <= m);
}

int main() {
    int n, m;
    cin >> n >> m;

    vector<int> v(n);

    for (int i = 0; i < n; i++) {
        cin >> v[i];
    }

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

    int low = 1, high = 3e8, ans = -1;

    while (low < high) {
        int mid = low + (high - low) / 2;

        if (verify(mid, n, m, v)) {
            ans = mid;
            high = mid - 1;
        } else {
            low = mid + 1;
        }

    }

    cout << ans << "\n";

    return 0;
}