Problem: Example

Input

2
10 10


Output

40.00000000

Solution (in CPP):

Solution:
#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
typedef pair<ll, ll> P;

#define EACH(i,a) for (auto& i : a)
#define FOR(i,a,b) for (ll i=(a);i<(b);i++)
#define RFOR(i,a,b) for (ll i=(b)-1;i>=(a);i--)
#define REP(i,n) for (ll i=0;i<(n);i++)
#define RREP(i,n) for (ll i=(n)-1;i>=0;i--)
#define debug(x) cout<<#x<<": "<<x<<endl
#define pb push_back
#define ALL(a) (a).begin(),(a).end()

const ll linf = 1e18;
const int inf = 1e9;
const double eps = 1e-12;
const double pi = acos(-1);

template<typename T>
istream& operator>>(istream& is, vector<T>& vec) {
	EACH(x,vec) is >> x;
	return is;
}
/*
template<class... T>
ostream& operator<<(ostream& os, tuple<T...>& t) {
	for (size_t i = 0; i < tuple_size< tuple<T...> >::value; ++i) {
		if (i) os << " ";
		os << get<0>(t);
	}
	return os;
}
*/
template<typename T>
ostream& operator<<(ostream& os, vector<T>& vec) {
	REP(i,vec.size()) {
		if (i) os << " ";
		os << vec[i];
	}
	return os;
}
template<typename T>
ostream& operator<<(ostream& os, vector< vector<T> >& vec) {
	REP(i,vec.size()) {
		if (i) os << endl;
		os << vec[i];
	}
	return os;
}

int main() {
	std::ios::sync_with_stdio(false);
	std::cin.tie(0);
    int n; cin >> n;
    vector<ld> v(n); cin >> v;
    vector<ld> x = v;
    FOR(i, 1, n) {
        REP(j, i) {
            ld dr = v[i] + v[j];
            ld dy = v[i] - v[j];
            ld dx = sqrt(dr * dr - dy * dy);
            x[i] = max(x[i], x[j]+dx);
        }
    }
    ld ans = 0;
    REP(i, n) {
        ans = max(ans, x[i] + v[i]);
    }
    cout << fixed << setprecision(10) << ans << endl;
}