#include<iostream>
#include<cstdio>
using namespace std;
int L,n, M;
const int N = 1e5 + 10;
int a[N];
bool check(int mid)
{
	int cnt = 0,now = 0;
	for (int i = 0; i < n; i++)
	{
		if (a[i]-now<mid)
		{
			cnt++;
		}
		else
		{
			now = a[i];
		}
		
	}
	return cnt <= M;
}
int binary_search(int l,int r)
{
	while (l <= r)
	{
		int mid = (l + r) >> 1;
		if (check(mid))
		{
			l=mid+1;
		}
		else
		{
			r = mid -1;
		}
	}
	return r;
}
int main()
{
	cin >> L >> n >> M;
	int ans, max = 0;
	for (int i = 0; i < n; i++)
	{
		scanf("%d", &a[i]);
	}
	cout << binary_search(1,L)<< endl;
}