freeCodeCamp/curriculum/challenges/english/10-coding-interview-prep/project-euler/problem-433-steps-in-euclids-algorithm.md

---
id: 5900f51d1000cf542c51002f
title: 'Problem 433: Steps in Euclid''s algorithm'
challengeType: 5
forumTopicId: 302104
dashedName: problem-433-steps-in-euclids-algorithm
---

# --description--

Let E(x0, y0) be the number of steps it takes to determine the greatest common divisor of x0 and y0 with Euclid's algorithm. More formally:x1 = y0, y1 = x0 mod y0xn = yn-1, yn = xn-1 mod yn-1

E(x0, y0) is the smallest n such that yn = 0.

We have E(1,1) = 1, E(10,6) = 3 and E(6,10) = 4.

Define S(N) as the sum of E(x,y) for 1 ≤ x,y ≤ N. We have S(1) = 1, S(10) = 221 and S(100) = 39826.

Find S(5·106).

# --hints--

`euler433()` should return 326624372659664.

```js
assert.strictEqual(euler433(), 326624372659664);
```

# --seed--

## --seed-contents--

```js
function euler433() {

  return true;
}

euler433();
```

# --solutions--

```js
// solution required
```