Problem: Example

Input

2
10 10


Output

40.00000000

Solution (in CPP):

Solution:
#include<bits/stdc++.h>
using namespace std;

#define int long long
typedef vector<int>vint;
typedef pair<int,int>pint;
typedef vector<pint>vpint;
#define rep(i,n) for(int i=0;i<(n);i++)
#define reps(i,f,n) for(int i=(f);i<(n);i++)
#define all(v) (v).begin(),(v).end()
#define each(it,v) for(__typeof((v).begin()) it=(v).begin();it!=(v).end();it++)
#define pb push_back
#define fi first
#define se second
template<typename A,typename B>inline void chmin(A &a,B b){if(a>b)a=b;}
template<typename A,typename B>inline void chmax(A &a,B b){if(a<b)a=b;}

int N;
double R[500];
double x[500];
signed main(){
    cin>>N;
    rep(i,N)cin>>R[i];
    x[0]=R[0];
    double ans=0;
    for(int i=1;i<N;i++){
        x[i]=R[i];
        for(int j=0;j<i;j++){
            double a=R[i]+R[j];
            double b=abs(R[i]-R[j]);
            double c=sqrt(a*a-b*b);
            chmax(x[i],x[j]+c);
        }
    }

    rep(i,N)chmax(ans,x[i]+R[i]);
    printf("%.20f\n",ans);
    return 0;
}