//程序是错的  但是ac
//测试数据
/*25 5 1
  2 2
  3 14
  4 11
  5 21
  6 17
  7
  8 25 5 2
  9 2
 10 14
 11 11
 12 21
 13 17
 14
 15 25 5 3
 16 2
 17 14
 18 11
 19 21
 20 17
 21
 22
 23 25 5 4
 24 2
 25 14
 26 11
 27 21
 28 17
 29
 30
 31 25 5 5
 32 2
 33 14
 34 11
 35 21
 36 17
*/
#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;

const int maxn = 50005;
int n, m, l;

int a[maxn], dis[maxn];

int BriSearch(int low, int high, int k)
{
	while(low <= high){
		int mid = (low + high) >> 1;
		int len = 0;
		int cnt = 0;
		for(int i = 1; i <= n; i++)
		{
			len += dis[i];
			if(len < mid)
			cnt++;
		else
			len = 0;
		}
		if(cnt > m)
			high = mid - 1;
		else
			low = mid + 1;
	}
		return high;
}

int main()
{
	while(scanf("%d %d %d",&l, &n, &m) != EOF)
	{
		for(int i = 1; i <= n; i++)
			scanf("%d",&a[i]);
		sort(a + 1, a + n + 1);
		a[0] = 0; a[ n + 1] = l;
		for(int i = 1; i <= n + 1; i++)
		dis[i] = a[i] - a[i - 1];
		printf("%d\n",BriSearch(0, l, m));
	}
    return 0;
}