#include <bits/stdc++.h>
using namespace std;

int n, m, s[10000000], a;

int chenk(int mid) {
	int jsq = 0, syg = 0;
	for (int i = 1; i <= n; ++i) {
		if (s[i] - syg >= mid)
			syg = s[i];
		else ++jsq;
	}
	return jsq;
}

int main() {
	int l = 2e9;
	cin >> a >> n >> m;
	for (int i = 1; i <= n; ++i)
		cin >> s[i], l = min(l, s[i] - s[i - 1]);
	int r = a;
	while (l <= r) {
		int mid = (l + r) / 2;
		int t = chenk(mid);
		if (t > m) r = mid - 1;
		else l = mid + 1;
	}
	cout << r;
	return 0;
}