90分求调玄关

#include<bits/stdc++.h>
#define ll long long
using namespace std;
	ll a,sum=2e9;
ll read(){
	char ch=getchar();
	ll s=0,w=1;
	while(ch<'0'||ch>'9'){
		if(ch=='-')w=-1;
		ch=getchar();
	}while(ch>='0'&&ch<='9'){
		s=s*10+ch-'0';
		ch=getchar();
	}return s*w;
}
int main(){
	a=read();
	ll b[a],c[a]={0},d[a]={0};//c=buy;d=sell
	for(int i=0;i<a-1;i++){
		b[i]=read();
		if(b[i]<sum)sum=min(sum,b[i]);
		c[i]=sum;
	}sum=0;
	for(int i=a-2;i>0;i--){
		sum=max(sum,b[i]);
		d[i]=sum;
	}sum=-1e10;
	for(int i=0;i<a-1;i++)sum=max(sum,d[i+1]-c[i]);
	cout<<sum;
	return 0;}