freeCodeCamp/curriculum/challenges/english/10-coding-interview-prep/project-euler/problem-339-peredur-fab-efrawg.md

---
id: 5900f4c01000cf542c50ffd2
title: 'Problem 339: Peredur fab Efrawg'
challengeType: 5
forumTopicId: 301997
dashedName: problem-339-peredur-fab-efrawg
---

# --description--

"And he came towards a valley, through which ran a river; and the borders of the valley were wooded, and on each side of the river were level meadows. And on one side of the river he saw a flock of white sheep, and on the other a flock of black sheep. And whenever one of the white sheep bleated, one of the black sheep would cross over and become white; and when one of the black sheep bleated, one of the white sheep would cross over and become black." - Peredur the Son of Evrawc

Initially, each flock consists of $n$ sheep. Each sheep (regardless of color) is equally likely to be the next sheep to bleat. After a sheep has bleated and a sheep from the other flock has crossed over, Peredur may remove a number of white sheep in order to maximize the expected final number of black sheep. Let $E(n)$ be the expected final number of black sheep if Peredur uses an optimal strategy.

You are given that $E(5) = 6.871346$ rounded to 6 places behind the decimal point.

Find $E(10\\,000)$ and give your answer rounded to 6 places behind the decimal point.

# --hints--

`peredurFabEfrawg()` should return `19823.542204`.

```js
assert.strictEqual(peredurFabEfrawg(), 19823.542204);
```

# --seed--

## --seed-contents--

```js
function peredurFabEfrawg() {

  return true;
}

peredurFabEfrawg();
```

# --solutions--

```js
// solution required
```