代码:

#include<bits/stdc++.h>
#define ll long long
using namespace std;
const ll N=50015;
ll n,a[N],L,m,l,r=1000000000;
bool check(ll mid){
	ll sum=0;
	for(ll i=2;i<n-1;i++){
		if(abs(a[i+1]-a[i])<=mid) sum++;
	}
	return sum<m;
}

int main(){
	cin>>L>>n>>m;
	for(ll i=1;i<=n;i++) cin>>a[i];
	while(l<r){
		ll mid=(l+r+1)>>1;
		if(check(mid)) r=mid-1;
		else l=mid;
	}
	cout<<l;
	return 0;
}