#include<bits/stdc++.h>
using namespace std;
const int N=1e5+10;
int L,n,m;
int a[N],l,r,ans;
bool check(int mid){
	int last=0;
	int sum=0;
	for(int i=1;i<=n;i++){
		if(a[i]-last<mid){
			sum++;
		}
		else{
			last=a[i];
		}
	}
	return sum<=m;
}
int main(){
	cin>>L>>n>>m;
	for(int i=1;i<=n;i++)
		cin>>a[i];
	a[++n]=L;
	r=L;
	while(l<=r){
		int mid=l+r>>1;
		if(check(mid)){
			ans=mid;
			l=mid+1;
		}
		else
			r=mid-1;
	}
	cout<<ans;

}
小鸟