#include<bits/stdc++.h>
using namespace std;
long long l,n,k,a[1000010],ans;
bool check(long long x){
	long long sum=0,w=0;
	for(long long i=2;i<=n;i++){
		if(a[i]-a[i-1]>x){
			if(a[i]-a[i-1]%x==0){
				sum+=(a[i]-a[i-1])/x-1;
			}else{
				sum+=(a[i]-a[i-1])/x;
			}
		}
	}
	if(sum<=k) return true;
	else return false;
}
int main(){
	cin>>l>>n>>k; 
	for(long long i=1;i<=n;i++){
		cin>>a[i];
	}
	long long left=1,right=l;
	while(left<=right){
		long long mid=(left+right)/2;
		if(check(mid)){
			ans=mid;
			right=mid-1;
		}else{
			left=mid+1;
		}
	}
	cout<<ans;
	return 0;
}

不知道为啥不对