#include<iostream>

 #include<cstdio>

 #include<cstring>

 #include<cmath>

 #include<algorithm>

 using namespace std;

 const int MAXN=+;

 int n,m;

 int pos[MAXN];

 int whether(int d)

 {

     int now=;

     int nowpos=pos[]+d;

     for (int i=;i<m;i++)

     {

         while (pos[now]<nowpos && now<n) now++;

         if (now==n)

         {

             return ;

         }

         nowpos=pos[now]+d;

     }

     return ;

 }

 int main()

 {

     scanf("%d%d",&n,&m);

     for (int i=;i<n;i++) scanf("%d",&pos[i]);

     sort(pos,pos+n);

     int lb=,ub=pos[n-];

     while (ub-lb>)

     {

         int mid=(lb+ub)/;

         if (whether(mid)) lb=mid;

         else ub=mid;

     }

     cout<<lb<<endl;

     return ;

 }