#include<bits/stdc++.h>
using namespace std;
int L,n,m,a[50004],l,r,ans;
bool check(int mid)
{
	int last=0,sum=0;
	for(int i=1;i<=n;i++)
		a[i]-last>=mid?last=a[i]:sum++;
	return sum<=m;
}
int main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
   	scanf("%d%d%d",&L,&n,&m);
   	for(int i=1;i<=n;i++)
   		scanf("%d",&a[i]);
   	a[++n]=L,l=1,r=L;
   	while(l<=r)
   	{
	   	int mid=(l+r)>>1;
	   	check(mid)?ans=mid,l=mid+1:r=mid-1;
	}
   	printf("%d",ans);
   	return 0;
}