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# Find the Duplicate Number (easy)

## Problem Statement

We are given an unsorted array containing `n+1`

numbers taken from the range `1`

to `n`

. The array has only one duplicate but it can be repeated multiple times. **Find that duplicate number without using any extra space**. You are, however, allowed to modify the input array.

**Example 1**:

```
Input: [1, 4, 4, 3, 2]
Output: 4
```

**Example 2**:

```
Input: [2, 1, 3, 3, 5, 4]
Output: 3
```

**Example 3**:

```
Input: [2, 4, 1, 4, 4]
Output: 4
```

**Constraints:**

`nums.length == n + 1`

- 1 <= n <= 10^5
`1 <= nums[i] <= n`

- All the integers in `nums

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