#define LOCAL

#undef _GLIBCXX_DEBUG

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

#define IOS ios::sync_with_stdio(false);cin.tie(0)
#define all(x) x.begin(), x.end()
#define ff first
#define ss second
#define MOD 1000000007LL
#define LLINF 100000000000000005LL
#define INF (int)1e9+1
#define pb push_back

// Copied from Gennady-Korotkevich's template

template <typename A, typename B>
string to_string(pair<A, B> p);

template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p);

template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p);

string to_string(const string& s) {
	return '"' + s + '"';
}

string to_string(const char* s) {
	return to_string((string)s);
}

string to_string(bool b) {
	return (b ? "true" : "false");
}

string to_string(vector<bool> v) {
	bool first = true;
	string res = "{";
	for (int i = 0; i < static_cast<int>(v.size()); i++) {
		if (!first) {
			res += ", ";
		}
		first = false;
		res += to_string(v[i]);
	}
	res += "}\n";
	return res;
}

template <size_t N>
string to_string(bitset<N> v) {
	string res = "";
	for (size_t i = 0; i < N; i++) {
		res += static_cast<char>('0' + v[i]);
	}
	return res;
}

template <typename A>
string to_string(A v) {
	bool first = true;
	string res = "{";
	for (const auto& x : v) {
		if (!first) {
			res += ", ";
		}
		first = false;
		res += to_string(x);
	}
	res += "}\n";
	return res;
}

template <typename A, typename B>
string to_string(pair<A, B> p) {
	return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}

template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p) {
	return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " + to_string(get<2>(p)) + ")";
}

template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p) {
	return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " + to_string(get<2>(p)) + ", " + to_string(get<3>(p)) + ")";
}

template <typename A, typename B, typename C, typename D, typename E>
string to_string(tuple<A, B, C, D, E> p) {
	return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " + to_string(get<2>(p)) + ", " + to_string(get<3>(p)) + "," + to_string(get<4>(p)) + ")";
}

void debug_out() {
	cerr << endl;
}

template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
	cerr << " " << to_string(H);
	debug_out(T...);
}

#ifdef LOCAL
#define debug(...) cerr << "\n[" << #__VA_ARGS__ << "]:\n", debug_out(__VA_ARGS__)
#else
#define debug(...) 42
#endif

// End of Gennady-Korotkevich's template 

using llong = long long;
using PII = pair<int, int>;
using db = double;

int n;
vector<double> p;
vector<vector<double>> dp;

double dfs(int h, int t) {
	int idx = h + t;
	if (idx == n && t >= (n + 1) / 2) return 0;
	if (idx == n) return 1;
	double& ret = dp[h][t];
	if (ret != -1) return ret;
	if (t >= (n+1) / 2) return ret = 0;
	ret = 0;
	ret += p[idx] * dfs(h + 1, t);
	ret += (1 - p[idx]) * dfs(h, t + 1);
	return ret;
}

int main() {
	IOS;
	cin >> n;
	dp = vector<vector<double>>(n, vector<double>(n, -1));
	p = vector<double>(n);
	for (int i = 0; i < n; i++) cin >> p[i];
	cout << fixed << setprecision(10);
	cout << dfs(0,0);
}

Measured memory_bytes: 74372