代码如下：

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

int k, n, m, l, r, mid;
int a[50001];

bool check(int x){
	int cnt = 0, now = 1;
	for (int i=1; i<=n; i++){
		if (a[i]-a[now] < x) cnt++;
		else now = i;
	}
	return cnt <= m;
}

int main(){
	ios::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
	
	cin >> k >> n >> m;
	for (int i=1; i<=n; i++) cin >> a[i];
	sort(a+1, a+n+1);
	
	r = k;
	while (l < r){
		mid = (l+r+1) >> 1;
		if (check(mid)) l = mid;
		else r = mid-1;
	}
	
	cout << l;
	
	return 0;
}