必关

#include <bits/stdc++.h>
using namespace std;
long long L, n, m;
long long d[50005];
bool calc(long long x) {
	long long cnt = 0, a = 0;
	for (int i = 1; i <= n; i++){
		if (d[i] - a < x)
			cnt++;
		else
			a = d[i];
	}
	if (L - a < x)
		cnt++;
	return cnt > m;
}
int main () {
	scanf("%lld%lld%lld", &L, &n, &m);
	for(int i = 1; i <= n; i++) {
		scanf("%lld",&d[i]);
	}
	long long l = 0, r = L;
	while (l < r) {
		long long mid = (l + r) / 2;
		if (calc(mid)) {
			r = mid;
		} else
			l = mid + 1;
	}
	printf ("%lld", l);
	return 0;
}