#1 RE，求助奆佬

#include<bits/stdc++.h>
using namespace std;
int a[10000010];
long n,k,ans,ri,le;
bool check(int mid){
	int sum=0;
	for(int i=1;i<n;i++){
		sum+=a[i]/mid;
		if(sum>k) return 0;
	}
	return sum<=k;
}
int main()
{
	scanf("%d%d%d",&ri,&n,&k);
	for(long i=1;i<=n;i++) scanf("%d",&a[i]);
	for(long i=1;i<n;i++) a[i]=a[i+1]-a[i]-1;
	while(le<=ri){
		int mid=(le+ri)>>1;
		if(check(mid)) ri=mid-1,ans=mid;
		else le=mid+1;
	}
	printf("%d\n",ans);
}