/* This solves the problem using linear search, which of course will be too slow,
   but it's a good first step to implementing binary search. */

#include <vector>
#include <iostream>
#include <algorithm>
#include <cstdio>
using namespace std;

class Solution {
  public:
    int minimizeMax(vector <int> &nums, int p);
};

int Solution::minimizeMax(vector <int> &nums, int p)
{
  int ans;
  int max;
  int num_pairs;
  int start, size;
  size_t i;

  sort(nums.begin(), nums.end());
  max = nums[nums.size()-1];
  start = 0;
  size = max+1;         // This is because the range of answers is [0,max].

  while (size > 1) {
    ans = start+size/2-1;
    num_pairs = 0;
    for (i = 1; i < nums.size(); i++) {
      if (nums[i] - nums[i-1] <= ans) {
        num_pairs++;
        i++;
      }
    }
    if (num_pairs >= p) {
      size /= 2;
    } else {
      start += size/2;
      size -= size/2;
    }
  }

  return start;
}

/* Read in nums and p, and call the method. */

int main()
{
  vector <int> nums;
  int p;
  Solution s;

  while (cin >> p) nums.push_back(p);
  nums.pop_back();
  cout << s.minimizeMax(nums, p) << endl;
  return 0;
}