#include <iostream>
#include <algorithm>
typedef long long ll;
using namespace std;
const int N = 1e5 + 10;
ll a[N], length, n, k;

bool mat(ll mid)
{
    ll count = 0;
    for (int i = 2; i <= n ; i++)
    {
        if (a[i] - a[i - 1] > mid)
        {
            count += (a[i] - a[i-1]) / mid;
            if ((a[i] - a[i - 1]) % mid == 0) count--;
        }
        //if (count > k) return false;
    }
    return count <= k;
}

ll find(ll l, ll r)
{
    while (l < r)
    {
        ll mid = r + l >> 1;
        if (mat(mid))
            r = mid;
        else
            l = mid + 1;
    }
    return l;
}

int main()
{
    cin >> length >> n >> k;
    for (int i = 1; i <= n; i++)
        cin >> a[i];
    ll l = 0, r = a[n];
    cout << find(l, r);

    return 0;
}