#include<iostream>
#include<cstdio>
#include<cstring>
#include<string>
#include<algorithm>
using namespace std;
const int maxn=100007;
const double eps=1e-8;
int n,c;
int x[maxn];
int le=1,ri,mid;
int main(){
    scanf("%d%d",&n,&c);
    for(int i=0;i<n;i++){
        scanf(
 
"%d",&x[i]);

    }
    sort(x,x+n);
    ri=x[n-1];
    int last=1;
    while(le<=ri){
        mid=(le+ri)/2;
        if(last==mid){
            break;
        }
        last=mid;

        int sum=x[0]+mid,cnt=1;
        for(int i=2;i<n;i++){
            if(sum<=x[i]){
                cnt
 
++;
                sum=x[i]+mid;
            }
        }
        if(cnt<c){
            ri=mid-1;
        }
        else
            le=mid+1;
    }
    printf("%d\n",r1);
    
}