Problem: Example

Input

2
10 10


Output

40.00000000

Solution (in CPP):

Solution:
#include "iostream"
#include "climits"
#include "list"
#include "queue"
#include "stack"
#include "set"
#include "functional"
#include "algorithm"
#include "string"
#include "map"
#include "unordered_map"
#include "unordered_set"
#include "iomanip"
#include "cmath"
#include "random"
#include "bitset"
#include "cstdio"
#include "numeric"
#include "cassert"
#include "ctime"

using namespace std;

constexpr long long int MOD = 1000000007;
//constexpr int MOD = 1000000007;
//constexpr int MOD = 998244353;
//constexpr long long int MOD = 998244353;
constexpr double EPS = 1e-12;

//int N, M, K, T, H, W, L, R;
long long int N, M, K, T, H, W, L, R;


int main() {
	ios::sync_with_stdio(false);
	cin.tie(0);

	cin >> N;
	vector<long double>v(N);
	for (auto &i : v)cin >> i;
	vector<long double>r(N);
	r[0] = v[0];
	for (int i = 1; i < N; i++) {
		r[i] = v[i];
		for (int j = 0; j < i; j++) {
			r[i] = max(r[i], r[j] + sqrt((v[i] + v[j])*(v[i] + v[j]) - (v[i] - v[j])*(v[i] - v[j])));
		}
	}
	long double ans = 0;
	for (int i = 0; i < N; i++) {
		ans = max(ans, r[i] + v[i]);
	}
	cout <<setprecision(20)<< ans << endl;
}