#include<iostream>
#include<cstdio>
using namespace std;
const int maxn=50010;
int len,n,m,a[maxn],ans;

bool check(int x)
{
	int cnt=0,sum=0;
	for(int i=1;i<=n+1;i++)
	{
		sum+=a[i]-a[i-1];
		if(sum<x)
			cnt++;
		else sum=0;
	}
	if(cnt>m)return 0;
	return 1;
}

int main()
{
	scanf("%d%d%d",&len,&n,&m);
	for(int i=1;i<=n;i++)
		scanf("%d",&a[i]);
	a[0]=0;a[n+1]=len;
	int l=0,r=len+1,mid;
	while(l<=r)
	{
		mid=(l+r)>>1;
		if(check(mid))
		{
			l=mid+1;
			ans=mid;
		}
		else r=mid-1;
	}
	printf("%d",ans);
	return 0;
}