# 1556. Thousand Separator

<https://leetcode.com/problems/thousand-separator>

## Description

Given an integer `n`, add a dot (".") as the thousands separator and return it in string format.

**Example 1:**

```
**Input:** n = 987
**Output:** "987"
```

**Example 2:**

```
**Input:** n = 1234
**Output:** "1.234"
```

**Example 3:**

```
**Input:** n = 123456789
**Output:** "123.456.789"
```

**Example 4:**

```
**Input:** n = 0
**Output:** "0"
```

**Constraints:**

* `0 <= n < 2^31`

## ac

```java
```