cd:
#include<bits/stdc++.h>
using namespace std;
const int N = 5e4 + 10;
int len, n, k;
int a[N];

bool check(int x)
{
    int cnt = 0;
    for(int i = 0, j = 1;i <= n + 1;i++)
    {
        int li = 0;
        while(a[i] + x > a[j] && j <= n + 1)
        {

            cnt++;
//          if(x == 9)cout << a[j] <<
            j++;
            li++;
        }
        j++;
        i += li;
    }
//  if(x == 9)
//  cout << cnt << endl;
    if(cnt > k)return false;
    return true;
}

int main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);

    cin >> len >> n >> k;
    for(int i = 1;i <= n;i++)cin >> a[i];
    a[n + 1] = len;

    int l = 1, r = len;
    while(l < r)
    {
        int mid = (l + r + 1) >> 1;
        if(check(mid))l = mid;
        else r = mid - 1;
    }
    cout << l;
    return 0;
}