import std.stdio, std.string, std.conv;
import std.range, std.algorithm, std.array, std.typecons, std.container;
import std.math, std.numeric, core.bitop;

enum inf = 10L^^15;
enum mod = 10L ^^ 9 + 7;

void main() {
    int n;
    scan(n);
    auto p = readln.split.to!(double[]);

    auto dp = new double[][](n + 1, n + 1);
    fillAll(dp, 0);
    dp[0][0] = 1;

    foreach (i ; 0 .. n) {
        foreach (j ; 0 .. n) {
            dp[i+1][j+1] += dp[i][j] * p[i];
            dp[i+1][j] += dp[i][j] * (1 - p[i]);
        }
    }

    debug {
        writefln("%(%s\n%)", dp);
    }

    double ans = 0;
    foreach (i ; (n + 1) / 2 .. n + 1) {
        ans += dp[n][i];
    }

    writefln("%.12f", ans);
}







void scan(T...)(ref T args) {
    import std.stdio : readln;
    import std.algorithm : splitter;
    import std.conv : to;
    import std.range.primitives;

    auto line = readln().splitter();
    foreach (ref arg; args) {
        arg = line.front.to!(typeof(arg));
        line.popFront();
    }
    assert(line.empty);
}


void fillAll(R, T)(ref R arr, T value) {
    static if (is(typeof(arr[] = value))) {
        arr[] = value;
    }
    else {
        foreach (ref e; arr) {
            fillAll(e, value);
        }
    }
}