'use strict';

process.stdin.resume();
process.stdin.setEncoding('utf-8');

let inputString = '';
let currentLine = 0;

process.stdin.on('data', inputStdin => {
    inputString += inputStdin;
});

process.stdin.on('end', _ => {
    inputString = inputString.trim().split('\n').map(string => {
        return string.trim();
    });

    main();
});

function readline() {
    return inputString[currentLine++];
}

function getArray(str) {
    return str.split(' ').map(x => Number(x));
}

function getInt(str) {
    return Number(str);
}

function getStrArray(str) {
    return str.split(' ').map(x => x);
}

function create2DArray(row, col, filler = 0) {
    return Array(row)
        .fill(filler)
        .map(() => Array(col).fill(filler));
}
// ---------------------------------------



function main() {
    let n = getInt(readline());
    let ar = getArray(readline());
    let arr = [0, ...ar];
    let dp = create2DArray(n+1, n+1, 0);
    dp[1][0] = 1-arr[1];
    dp[1][1] = arr[1];
    for (let i = 2; i <= n; ++i) {
        dp[i][0] = dp[i][0]* (1-arr[i]);
    }

    for (let i = 2; i <= n; ++i) {
        dp[i][i] = dp[i - 1][i - 1] * arr[i];
    }
    

    for(let i=1; i <= n; ++i) {
        for (let j = 1; j < i; ++j) {
            dp[i][j] = dp[i-1][j-1]*arr[i] + dp[i-1][j]*(1-arr[i])
        }    
    }

    let ans = 0;

    for (let i = Math.ceil(n/2); i <= n; ++i) {
        ans +=dp[n][i];
    }
    console.log(ans);
} 

/*

dp[i][j] = dp[i-1][j-1]*pj +  dp[i-1][j]*(1-pj)








*/