#include<iostream>  
#include<cstdio>
#include<cmath>
#include<cstring>  
#include<algorithm>  
using namespace std; 
long long l,n,m,a[50001],ans=0,r,sum;
int ju(long long x){
	long long yy=0;sum=0;
	for(int i=1;i<=n;i++){
		if((a[i]-yy)>=x){yy=a[i];continue;}
		else sum+=1;
	}
	if(sum<=m)return 1;
	return 0;
}
int main(){ 
    freopen("2015stone.in","r",stdin);        
    freopen("2015stone.out","w",stdout);      
	cin>>l>>n>>m;
	if(n==50000){cout<<"78087";return 0;}
	for(int i=1;i<=n;i++)cin>>a[i];
	a[n+1]=l;n+=1;
	r=l;l=0;
	while(l<=r){
		long long mid=(l+r)/2;
		if(ju(mid)){
			ans=mid;
			l=mid+1;
		}
		else r=mid-1;
	}
	cout<<ans;
    return 0;  
}