#pragma comment(linker, "/stack:247474112")
#pragma GCC optimize("Ofast")

#include<bits/stdc++.h>
 
using namespace std;
 
#define sz(x) x.size()
#define clr(x) x.clear()
#define mem(x ,y) memset(x , y , sizeof x )
#define all(a ) a.begin() , a.end()
#define pb push_back
#define mp make_pair
#define ff first
#define ss second
#define pii pair<int , int>
#define endl "\n"
#define fast()   ios_base :: sync_with_stdio(false ) ; cin.tie(0) ; cout.tie(0) ;
#define dbg(args...) do {   cerr << #args << ' ' ;  print(args); } while(0); cerr<< endl ;
#define dbgv(v ) rep(i, sz(v) )  cerr << v[i] << ' ' ;  cout << endl ;
#define dbga(x, n) rep(i , n ) cerr << x[i] << ' ' ;  cout << endl
#define forn(i,a,n ) for(int  i = a ; i <= n ; i++ )
#define rep(i ,n ) for(int i = 0 ; i < n ; i++ )
#define repi(i ,n ) for(int i = 1 ; i <= n ; i++ )
#define repit(i, c) for( __typeof((c).begin()) i = (c).begin(); i != (c).end();++i )
#define si(a) scanf("%d",&a )
#define sl(a) scanf("%I64d",&a )
#define sd(a) scanf("%lf",&a )
#define sii(a , b) scanf("%d %d",&a , &b )
#define siii(a , b , c) sii(a, b ) ; si(c) ;
#define sdd(a , b) scanf("%lf %lf",&a , &b )
#define sll(a , b) scanf("%I64d %I64d",&a , &b )
#define wri(a )  printf("%d\n" , a ) ;
#define wrii(a ,b ) printf("%d %d\n" , a,  b ) ;
#define wrl(a )  printf("%I64d\n" , a ) ;
#define CASE(c ) printf("Case %d: " ,c) ;
const long long  mod = 1e9+7 ;
const int inf = 1e9  ;
const long long  lnf = 1e18 ;
 
int setbit(int n, int pos  ) { return n = n|(1<< pos) ; }
int resetbit(int n,int pos ) {  return n =  n & ~(1<<pos ); }
bool checkbit(int n,int pos ) { return (bool ) (n& (1<<pos))  ; }

template< typename T > void print(const T& v) {    cerr << v << ' ' ;}
template<typename  T> T modMul(T x, T y ) { x %= mod ; y %= mod ; return (x*y)%mod  ;  }
template<typename  T> T modAdd(T x, T y  ) { x %= mod ; y %= mod ; return (x+y)%mod ;  }
template< typename T1, typename... T2 > void print( const T1& first, const T2&... rest ){ print(first); print(rest...) ;}
template<typename  T> T modPow(T x, T k ) { if(k == 0 ) return 1; if(k&1  ) { return ( (x%mod)*modPow(x,k-1, mod )%mod )%mod ; } else { T ret = modPow(x,k/2 , mod ) ; ret %= mod ; return (ret*ret )%mod; } }
template<typename T> T ext_gcd(T num1 , T num2, T &X , T &Y ) { T r2,r1, q2, q1 , x2, x1, y2 ,y1 , x,  y, r   ; x2 = 1; y2 = 0;  x1 = 0; y1 = 1; for( r2 =num1 ,r1 = num2 ;r1 != 0 ; y2 = y1, y1 = y,x2 = x1 ,x1 = x ,r2 = r1, r1 = r) {q1 = r2/r1; x = x2 - q1*x1; y = y2 - q1*y1; r = r2%r1 ; } X = x2 ; Y = y2 ; return r2 ;  } 

template<typename T >
T modInv( T x , T m ) {  
    return modPow(x,m-2 , m) ; 
    long long ret, t ;
    ext_gcd( x, m ,ret ,t  ) ;
    ret %= m ;
    if(ret<0) ret += m  ;
    return ret;
}

typedef long long ll  ;
typedef unsigned long long  ull ;
typedef vector<int> vi  ;

//int dx[] = {0 , 0 ,+1, -1 } ;
//int dy[] = {-1, +1,0 , 0 };
/*
ll  prime[400] ; 
vector<ll> v  ; 
ll dp[M+2]  ,  a[M+2];

void  seive() {
    int cnt =0; 
    for(ll i=2 ; i<=300  ; i++ ) {
        if(prime[i]==0LL ) {
            for(ll j=i*i ; j<= 300; j += i ) {
                prime[j] = 1LL ; 
                
            }
        }
    }

    forn(i,2 , 300) if(prime[i] == 0LL ) v.pb(i) ; 
    //dbg(sz(v) ) ;
    //return cnt;  
}


*/
 
/////////////////////////////////////  code from here ///////////////////////////////////////////////////

const int M = 200002 ;  
//const ll N = 1e1 ;
//const int N =10;

double dp[3002][3002] ,a[3499];
int lim, n ;

double func(int id,int cnt) {
    if(id>=n ) {
        return ( cnt>=lim );

    }
    double &ans =dp[id][cnt] ;
    if(ans>-1.0) return ans ;
    ans = 0.0; 

    ans += func(id+1,  cnt)*(1.0-a[id]) ;
    ans += func(id+1, cnt+1)*a[id] ;


    return ans ;
}
void solve() {
    si(n ) ; 
    rep(i ,n ) sd(a[i] ) ;
    
    rep(i,3001 ) rep(j ,3001 ) dp[i][j] = -1.0; 
    lim = n/2; 
    lim++; 
    printf("%.10lf\n", func(0,0) ) ;


}
 
int main() {

       // freopen("in.txt", "r", stdin  );
    // freopen( "out.txt", "w",stdout );     
    //fast(); 
    int t=1; 
    // si(t) ;
    while( t-- ){
        solve() ;
    }

    return 0 ;

}

 
 
    

Measured memory_bytes: 70912