#include <bits/stdc++.h>
#define ll long long
using namespace std;
const int N = 100005;
int n, m, k, s, t, K, L, a[N];
int check(int x){
	int ans = 0;
	for (int i = 1; i < n; ++i){
		int len = a[i + 1] - a[i];
		if (len % x == 0) ans += len / x - 1;
		else ans += len / x;
	}
	return ans <= K;
}
int main(){
	cin >> L >> n >> K;
	for (int i = 1; i <= n; ++i)
		cin >> a[i];
	sort(a + 1, a + 1 + n);
	int l = 1, r = L;
	while (l <= r)
	{
		int mid = (l + r) / 2;
		if (check(mid)) r = mid - 1;
		else l = mid + 1;
	}
	cout << l;
}