#include <iostream>
#include <stdio.h>
#include <vector>
#include <algorithm>
using namespace std;
int n, c;
long long tmp;
long long ans=0;
vector<long long> v;
void go(long long start, long long finish) {
	if (start > finish) return;
	long long distance = start - ((start - finish) / 2);
	long long cntt = 1;
	long long before = v[0];
	for (int i = 1; i < v.size(); i++) {
		if (before + distance <= v[i]) {
			before = v[i];
			cntt++;
			//printf("%d ", v[i]);
		}
		if (cntt > c) {
			break;
		}
	}
	//이분탐색을 공유기 갯수 기준으로 가르기
	if (cntt >= c) {
		if (distance > ans) {
			ans = distance;
		}
		go(distance + 1, finish); //이분탐색을 할 때는 거리를 조절
	}
	else {
		go(start, distance - 1);
	}
}
int main() {
	scanf("%d %d", &n, &c);
	for (int i = 0; i < n; i++) {
		scanf("%lld", &tmp);
		v.push_back(tmp);
	}
	sort(v.begin(), v.end());
	//printf("%d\n", v[n - 1] - v[0]);
	go(1,v[n-1]-v[0]);
	printf("%d\n", ans);
	return 0;
}