#include <iostream>
#include <algorithm>
#include <deque>
using namespace std;
const int Nmax = 1e6 + 1;
int v[Nmax];
int n, a, b, sol = -1;
bool ver(int dif)
{
deque <int> q;
q.push_back(0);
int i = a;
while(i <= n && !q.empty())
{
if(i - q.front() >= a)
{
if(i - q.front() <= b && v[i] - v[q.front() + 1] <= dif)
{
q.push_back(i);
i++;
}
else
q.pop_front();
}
else
i++;
}
if(!q.empty() && q.back() == n)
{
return true;
}
return false;
}
int main()
{
int i;
cin >> n >> a >> b;
for(i = 1; i <= n; i++)
cin >> v[i];
sort(v + 1, v + n + 1);
int st = 0, dr = v[n];
while(st <= dr)
{
int mij = (st + dr) / 2;
///cout << "uite " << mij << '\n';
if(ver(mij))
{
dr = mij - 1, sol = mij;
}
else
st = mij + 1;
}
/*if(ver(sol - 1))
sol--;*/
cout << sol;
}
