#include <bits/stdc++.h>
using namespace std;
int l,n,m;
int a[50001];
bool f(int x){
	int sum=0,k=0;
	for(int i=0;i<n;i++){
		if(a[i]-k<x){
			sum++;
			k=a[i];
		}
		else k=a[i];
	}
	return sum<m;
}
int main(){
	cin>>l>>n>>m;
	for(int i=0;i<n;i++){
		cin>>a[i];
	}
	int le=0,r=n,mid;
	while(le<r){
		mid=le+r>>1;
		if(f(mid))le=mid+1;
		else r=mid-1;
	}
	cout<<le;
}