#include<bits/stdc++.h>				
using namespace std;
long long l,n,k,a[10000001];
long long s(long long x)
{
	int s = 0;
	for (int i = 1;i < n;i++)
	{
		s += (a[i] - a[i - 1]) / x;
	}
	return k >= s;
}
long long f()
{
	long long l = 0,r = 1000000,mid,c = -1;
	while (l <= r)
	{
		mid = (l + r) / 2;
		if (s(mid))
		{
			c = mid;
			r = mid - 1;
		}
		else
		{
			l = mid + 1;
		}
//				cout<<l<<" "<<r<<" "<<mid<<" "<<s(mid)<<endl;
	}
	return c;
}

int main()
{
	cin>>l>>n>>k;
	for (int i = 0;i < n;i++)
	{
		cin>>a[i];
	}
	cout<<f();
	return 0;

}

刚学二分，求助aaa