链接：https://www.luogu.org/problem/show?pid=3382

#include<iostream>
#include<cstring>
#include<cstdio>
#include<algorithm>
using namespace std;
double l,r;
int n;
const double eps=1e-7;
double a[1000];
double f(double x)
{
    double ans=a[1];
    for(int i=2;i<=n+1;i++)
        ans=ans*x+a[i];
    return ans;
}
int main()
{
    scanf("%d%lf%lf",&n,&l,&r);

    for(int i=1;i<=n+1;i++) scanf("%lf",&a[i]);
    double ll=l,rr=r,midx,midy;
        while(rr-ll>eps)
        {
            midx=(2*ll+rr)/3;
            midy=(ll+2*rr)/3;
            if(f(midx)<f(midy)) ll=midx;
            else rr=midy;
        }
    printf("%.5lf\n",ll);
    return 0;
}