Problem: Example

Input

2
10 10


Output

40.00000000

Solution (in CPP):

Solution:
#include <bits/stdc++.h>
#define syosu(x) fixed<<setprecision(x)
using namespace std;
typedef long long ll;
typedef unsigned int uint;
typedef unsigned long long ull;
typedef pair<int,int> P;
typedef pair<double,double> pdd;
typedef pair<ll,ll> pll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<double> vd;
typedef vector<vd> vvd;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<string> vs;
typedef vector<P> vp;
typedef vector<vp> vvp;
typedef vector<pll> vpll;
typedef pair<int,P> pip;
typedef vector<pip> vip;
const int inf=1<<29;
const ll INF=1ll<<60;
const double pi=acos(-1);
const double eps=1e-9;
const ll mod=1e9+7;
const int dx[4]={-1,0,1,0},dy[4]={0,-1,0,1};



int main(){
	ios::sync_with_stdio(0);
	cin.tie(0);
	int n;
	cin>>n;
	vd a(n),x(n);
	for(auto &i:a) cin>>i;
	x[0]=a[0];
	double res=2*a[0];
	for(int i=1;i<n;i++){
		x[i]=a[i];
		for(int j=0;j<i;j++){
			x[i]=max(x[i],x[j]+sqrt((a[i]+a[j])*(a[i]+a[j])-(a[i]-a[j])*(a[i]-a[j])));
		}
		res=max(res,x[i]+a[i]);
	}
	cout<<syosu(9)<<res<<endl;
//	for(auto i:x) cout<<i<<' ';cout<<endl;
}