#include <algorithm>
#include <iostream>
using namespace std;
int main()
{
    int n,bus,must,ans=0;
    int a[100000];
    cin>>n>>bus>>must;
    for(int i=0;i<n;i++){
        cin>>a[i];
    }
    sort(a,a+n);
    for(int i=must-1;i<n;i+=must){
        int now=a[i]-a[i+1-must];
        if(now>ans){
            ans=now;
        }
    }
    cout<<ans;
}