#include <bits/stdc++.h>

using namespace std;
const int maxN = 50005;
int l, n, m;
int L = 1, R, M;

int main() {
	cin >> l>> n>> m;
	int a[maxN], now, before = 0;
	for (int i = 0; i < n; i++) {
		cin >> now;
		a[i] = now - before;
		before = now;
	}
	a[n] = l - before;
	if (n == m) {
		cout << l;
		return 0;
	}
	R = l / (n - m);
	while (L <= R) {
		M = (L + R) / 2;
		int tmp, i, k = 0;
		for (i = 0; i <= n; i++) {
			tmp = a[i];
			while (tmp < M && i < n) {
				i++;
				tmp += a[i];
				k++;
			}
		}
		if (k <= m)
			L = M + 1;
		else
			R = M - 1;
	}
	cout << R;
	return 0;
}