#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define mt make_tuple
#define ll long long
#define eb emplace_back
#define fi first
#define pb push_back
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define forn(i, n) for (int i = 0; i < (int)(n); ++i)
#define fore(i, a, b) for (int i = (int)(a); i <= (int)(b); ++i)
#define scanVec(vec , n) for(int i = 0; i < n ; i++){ cin>>vec[i];}
#define printVec(vec , n) for(int i = 0; i < n ; i++){ cout<<vec[i]<<" ";}
#define mod(a,b) ((a%b +b)%b)
#define bit(x,i) (x&(1<<i))  //select the bit of position i of x
#define lowbit(x) ((x)&((x)^((x)-1))) //get the lowest bit of x
#define hBit(msb,n) asm("bsrl %1,%0" : "=r"(msb) : "r"(n)) //get the highest bit of x, maybe the fastest
#define max(a,b) (a<b?b:a)
#define min(a,b) (a>b?b:a) 
#define error(args...) { string _s = #args; replace(_s.begin(), _s.end(), ',', ' '); stringstream _ss(_s); istream_iterator<string> _it(_ss); err(_it, args); }
#define IN(i,l,r) (l<i&&i<r)
#define LINR(i,l,r) (l<=i&&i<=r)
#define LIN(i,l,r) (l<=i&&i<r)
#define INR(i,l,r) (l<i&&i<=r)
#define lastEle(vec) vec[vec.size()-1] 
#define SZ(x) ((int)((x).size()))
#define FOREACH(i,t) for (typeof(t.begin()) i=t.begin(); i!=t.end(); i++) 
#define ll long long 
#define ull unsigned long long
#define ui unsigned int
#define us unsigned short
#define INF 1001001001
#define PI 3.1415926535897932384626
 
using namespace std;
 using namespace __gnu_pbds;
 template <typename T>
 using ordered_set =
    tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
 
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<pii> vpi;
typedef vector<vi> vvi;
 
void err(istream_iterator<string> it) {}
template<typename T, typename... Args>
void err(istream_iterator<string> it, T a, Args... args) {
    cerr << *it << " = " << a << endl;
    err(++it, args...);
}
 
//----------------------------------------------------------------------------------------------------------------------
  
  
void swap(char &a, char & b){
    char temp = a;
    a = b;
    b = temp;
 
}
 
const ll MOD = 1e9 + 7;
const int MAXN = 1e3 + 5;
 
vector< int > graph[MAXN];
int in_degrees[MAXN];
int dist[MAXN];
bool visited[MAXN];
ll inf = 1e18*1LL;


//char grid[MAXN][MAXN];

void add_self(int &a, int b){
    a+= b;
    while(a > MOD){
        a-=MOD;
    }
}

int main(){
    int n;
    cin >> n;
    // vector< long double > dp(n + 1);
    // // 
    // dp[0] = 1;
    // for(int coin = 0; coin < n;coin++){
    //     double p_heads;
    //     cin >> p_heads;
    //     for(int i = coin + 1; i >= 0;i--){
    //         dp[i] = (i == 0 ? 0 : dp[i-1]*p_heads) + dp[i]*(1-p_heads);
    //     }
    // }
    // long double ans = 0;
    // for(int heads = 0;heads <= n;heads++){
    //     int tails = n - heads;
    //     if(tails < heads){
    //         ans += dp[heads];
    //     }
    // }
    // cout.precision(10);
    // cout << ans << endl;
    vector < vector< long double> > dp (n + 1,vector< long double > (n + 1));
    dp[0][0] = 1;
    vector < long double > prb (n);
    scanVec(prb,n);
    for(int i = 1;i <= n;i++){
        for(int j = 0;j <= i;j++){
            if(j) dp[i][j] += dp[i-1][j-1]*prb[i-1];
            dp[i][j] += dp[i-1][j]*(1 - prb[i-1]);
        }
    }
    long double ans = 0;
    for(int i = 0;i <= n;i++){
        if(n - i < i) {
         //cout << dp[n][i] << endl;
            ans += dp[n][i];
        }
    }
    cout.precision(10);
    cout << ans << endl;
    return 0;
}

Measured memory_bytes: 141056