#include <bits/stdc++.h>
using namespace std;
int n, L, k, a[100010];
bool check(int mid) {
	int y = k;
	int p = 0;
	for (int i = 2; i <= n; i++) {
		if (a[i] - p <= mid)
			p = a[i];
		else {
			p += mid;
			--i, --y;
		}
	}
	if (y >= 0)
		return true;
	else
		return false;
}
int main () {
	cin >> L >> n >> k;
	for (int i = 1; i <= n; i++)
		cin >> a[i];
	int r = L + 1, l = 1;
	while (l + 1 < r) {
		int mid = (l + r) / 2;
		if (check(mid))
			r = mid;
		else
			l = mid;
	}
	cout << r;
	return 0;
}