#include <bits/stdc++.h>
#include <cstdio>
using namespace std;
int L,n,k,a[200005],l=1,r;
int check(int mid){
	int cnt=0;
	for(int i=2;i<=n;i++){
		if(a[i] - a[i-1] > mid) cnt+= (a[i]-a[i-1] -1) / mid;
	}
	return cnt<=k;
}
int main()
{
	cin>>L>>n>>k;
	for(int i=1;i<=n;i++){
		scanf("%d",&a[i]);
	}
	sort(a,a+n+1);
	r=L;
	while(l<r){
		int mid=(l+r+1)>>1;
		if(check(mid)){
			r=mid-1;
		}	
		else l=mid;
	}
	cout<<l+1;
    return 0;
}