#include<bits/stdc++.h>
using namespace std;
const int maxl=1e9+10,maxn=5e4+10;
int ll,m,n,a[maxn];

inline int read(){
	int x=0,f=1;
	char c=getchar();
	while(c>'9'||c<'0'){
		if(c=='-')f=-1;
		c=getchar();
	}
	while(c>='0'&&c<='9'){
		x=((x<<1)+(x<<3))+c-'0';
		c=getchar();
	}
	return x*f;
}

inline bool check(int x){
	int now=0,sum=0;
	for(int i=1;i<=n+1;i++){
		if(a[i]-a[now]<x) sum++;
		else now=i;
	}
	return sum<=m;
}

inline void Init(){
	ll=read(),n=read(),m=read();
	for(int i=1;i<=n;i++)a[i]=read();
	a[n+1]=ll;
	a[0]=0;
}

inline void Work(){
	int l=1,r=ll;
	while(l<r){
		int mid=(l+r+1)>>1;
		if(check(mid))l=mid;
		else r=mid-1;
	}
	cout<<l<<endl;
}

int main(){
	Init();
	Work();
	return 0;
}