题目

#include<bits/stdc++.h>
using namespace std;
int n,mp[20010];
int u,s;
int ans=-1;
bool check(int x){
	int maxx[20010]={0},minn[20010]={0};
	maxx[1]=minn[1]=mp[1];
	for(int i=2;i<=n;i++){
		maxx[i]=min(mp[i],mp[1]-minn[i-1]);
		minn[i]=max(0,mp[i]-x+mp[1]+mp[i-1]-maxx[i-1]);
	}
	if(!minn[n]){
		return 1;
	}
	return 0;
}
void er_fen(){
	int l=u;
	int r=s;
	while(l<r){
		int mid=(l+r)>>1;
		if(check(mid)){
			r=mid-1;
		}
		else{
			l=mid+1;
		}
	}
	ans=l;
}
int main(){
	cin>>n;
	for(int i=1;i<=n;i++){
		cin>>mp[i];
		u=max(u,mp[i]);
		s=s+mp[i];
	}
	er_fen();
	cout<<ans;
}