Prepare

#include <bits/stdc++.h>
#define memset(a,b) memset(a,b,sizeof a)
#define eps 1e-6
using namespace std;
int n;
int m[11111];
double ans,sum1[11111],sum2[11111],mn1[11111],mn2[11111],a[11111];
inline bool check(double x) {
	memset(mn1,127);
	memset(mn2,127);
	for(int i=1;i<=n;i++)
		a[i]=m[i]-x;
	for(int i=1;i<=n;i++)
		sum1[i]=sum1[i-1]+a[i],mn1[i]=min(sum1[i],mn1[i-1]);
	for(int i=n;i;i--)
		sum2[i]=sum2[i+1]+a[i],mn2[i]=min(sum2[i],mn2[i+1]);
	for(int i=1;i<n-1;i++)
		if(mn1[i]+mn2[i+2]<=0)
			return 1;
	return 0;
}
int main() {
	scanf("%d",&n);
	for(int i=1;i<=n;i++)
		scanf("%d",m+i);
	double l=1,r=10000;
	while(r-l>eps) {
		double mid=(l+r)/2;
		if(check(mid))
			r=mid-eps,ans=mid;
		else
			l=mid+eps;
	}
	printf("%.3lf\n",ans);
	return 0;
}

<div class="cnblogs-markdown">
{0}
</div>

// Custom styles.
// Updated at 2019.02.22 by ShawnZhou
.post {
	margin-top: 60px;
	margin-bottom: 60px;
	padding: 25px;
    -webkit-box-shadow: 0 0 5px rgb(255, 255, 255);
    -moz-box-shadow: 0 0 5px rgba(202, 203, 204, .5);
   
}

.site-meta {
    background: url(https://s2.ax1x.com/2019/02/16/kseaVI.jpg);
    background-size: 100% auto;
}


.post-block {
    background: rgba(247, 255, 254, 0.7);
}

.comments {
    background: rgba(247, 255, 254, 0.7);    
}

.footer {
    color: #00f145;
}

.posts-expand .post-meta {
    color: #4079ee;
}

.site-subtitle {
    color: #fff;
}

body { 
    @media (max-width: 1080px) {
      background-image: url(https://s2.ax1x.com/2019/02/16/ksekCT.jpg);
      background-attachment: fixed;
      background-repeat: no-repeat;
      background-size: 100% 100%; 
    }
    @media (min-width: 1080px) {
      background-image: url(https://s2.ax1x.com/2019/02/16/kseVv4.jpg);
      background-attachment: fixed;
      background-repeat: no-repeat;
      background-size: 100% 100%; 
    }
  
}

.header-inner {
    background: url(https://s2.ax1x.com/2019/02/16/kseeKJ.jpg);
    background-size: 100% 100%;
}

.sidebar-inner {
    background: #d0ed5a;
    background: url(https://s2.ax1x.com/2019/02/16/kseeKJ.jpg);
    background-size: 100% 100%;    
}

.menu-item-active a {
    background: #d0ed5a;
    border-bottom-color: #d0ed5a;
}

.site-description {
    color: #000;
}

.site-state-item-name {
    color: #0058ff;
}

.pagination {
    background: #d0ed5a;
}

.pagination .page-number.current {
    background: #00beff;
    border-top-color: #00beff;
}