Problem: Example

Input

2
10 10


Output

40.00000000

Solution (in CPP):

Solution:
#define  _CRT_SECURE_NO_WARNINGS
#pragma comment (linker, "/STACK:526000000")

#include "bits/stdc++.h"

using namespace std;
typedef string::const_iterator State;
#define eps 1e-11L
#define MAX_MOD 1000000007LL
#define GYAKU 500000004LL

#define MOD 998244353LL
#define seg_size 262144*2LL
#define pb push_back
#define mp make_pair
typedef long long ll;
#define REP(a,b) for(long long (a) = 0;(a) < (b);++(a))
#define ALL(x) (x).begin(),(x).end()

unsigned long xor128() {
	static unsigned long x = 123456789, y = 362436069, z = 521288629, w = time(NULL);
	unsigned long t = (x ^ (x << 11));
	x = y; y = z; z = w;
	return (w = (w ^ (w >> 19)) ^ (t ^ (t >> 8)));
}

void init() {
	iostream::sync_with_stdio(false);
	cout << fixed << setprecision(20);
}

#define int ll
void solve(){
	int n;
	cin >> n;
	vector<pair<long double, long double>> inputs;
	REP(i, n) {
		long double rad;
		cin >> rad;
		long double x = rad;
		REP(q, inputs.size()) {
			long double now_go = inputs[q].second;
			now_go += sqrt(pow(rad + inputs[q].first, 2) - pow(rad - inputs[q].first, 2));
			x = max(x, now_go);
		}
		inputs.push_back(mp(rad, x));
	}
	long double ans = 0;
	REP(i, inputs.size()) {
		ans = max(ans, inputs[i].first + inputs[i].second);
	}
	cout << ans << endl;
	return;
}

#undef int
int main() {
	init();
	solve();
}