...........................SOS............................

/*
Phạm Quang Thiện ^-^
fb: Phạm Thiện
titok: phamquangthien

*/


#include<bits/stdc++.h>

#define ll long long
#define el cout<<"\n"
#define FOR(i, l, r) for (int i=l; i<=r; i++)
#define FORE(i, l, r) for (int i=l; i<r; i++)
#define FORU(i, l, r) for(int i = r; i >= l; i--)
#define maxn 1007
#define tk "TPS"
#define tm cerr << (1.0 * clock() / CLOCKS_PER_SEC) << "s.";

using namespace std;


ll n, k, kk[maxn];


bool check(ll r)
{
    ll ans = 0, c = -1;

    FOR (i, 1, n)
    {
        if (kk[i] > c)
        {
            ans++;
            c = kk[i] + 2 * r;
        }


        if (ans > k)
            return false;

    }

    return true;
}


void input()
{
    cin >> n;


    FOR (i, 1, n)
        cin >> kk[i];

    cin >> k;

}


void solve ()
{
    sort (kk + 1, kk + n + 1);
    ll left = 0, right = 1000000, ans = -1;


    while (left <= right)
    {
        ll mid = left + (right - left) / 2;

        if (check(mid))
        {
            ans = mid;
            right = mid - 1;
        }


        else
            left = mid + 1;

    }

    if ((ans + 1) >= 1000000 / 2)
    {
        cout << 1;
        return;
    }


    cout << ans;

}


/* Authors: Pham Quang Thien from Gia Phu Secondary School Ninh Binh */


signed main()
{
    ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);


    if (fopen(tk".inp", "r"))
    {
        freopen(tk".inp", "r", stdin);
        freopen(tk".out", "w", stdout);
    }


    ll tt = 1; // cin >> tt;


    while (tt--)
    {
        input();
        solve();

    }


    el;
    tm

}