#include<cstdio>
#include<algorithm>
using namespace std;
const int N=1e5+5;
int L,n,k;
int a[N];
int read(){
	int x=0,f=1;
	char ch=getchar();
	while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}
	while(ch>='0'&&ch<='9')
		x=x*10+ch-'0',ch=getchar();
	return x*f;	
}
bool check(int dis){
	int num=0;
	for(int i=2;i<=n;++i){
		if( (a[i]-a[i-1]) <= dis)continue;
		if((a[i]-a[i-1])/dis*dis==(a[i]-a[i-1]))
			num+=((a[i]-a[i-1])/dis+1);
		else
			num+=(a[i]-a[i-1])/dis;
		if(num>k)return 0;
	}
//	printf("[%d %d]\n",dis,num);
	
	return 1;
}
int main(){
	L=read(),n=read(),k=read();
	for(int i=1;i<=n;++i)
		a[i]=read();
	sort(a+1,a+1+n);
	int l=1,r=2*L;
	int mid;
	while(l<r){
		mid=(l+r)/2;
		if(check(mid))
			r=mid;
		else
			l=mid+1;
//		printf("%d %d\n",l,r);
	}
	printf("%d\n",(l+r)/2);
	return 0;
}