/*
int      %o/%lo 8 %d/%i/%ld/%li 10 %x/%lx 16
longlong %lld
float    %f/%e
double   %lf/%le
char     %c
char[]   %s
'a'=97
'z'=122
'A'=65
'Z'=90
'0'=48
'9'=57
*/
#include <iostream>
#include <iomanip>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <ctime>
#include <limits>
#include <assert.h>
#include <stdlib.h>
using namespace std;
#define LL long long
#define ull unsigned long long
const int N=1e5+10;
const int INF=0x3f3f3f3f;
const double pi=3.1416;
int L,n,m,a[N],ans,l,r;
bool check(int mid){
	int last=0,sum=0;
	for(int i=1;i<=n;i++){
		if(a[i]-last<mid){
			sum++;
		}else{
			last=a[i];
		}
	}
	return sum<=m;
}
int main(){
	cin>>L>>n>>m;
	for(int i=1;i<=n;i++){
		cin>>a[i];
	}
	a[++n]=L;
	l=1,r=L;
	while(l<=r){
		int mid=(l+r)>>1;
		if(check(mid)){
			ans=mid;
			l=mid+1;
		}else{
			r=mid-1;
		}
	}
	cout<<ans;
return 0;
}