Missing Number

Interview

Time limit1sMemory limit512 MB

Summary

A string lists the numbers 1 to n in order with one number erased; find the missing value.

Level: Easy2 of 10
Topics: String, Implementation, Brute force
Solved: No attempts yet

Problem

You are teaching kindergarten! You wrote down the numbers from $1$ to $n$ , in order, on a whiteboard. While you were not paying attention, one of your students erased one of the numbers.

Can you tell which number your mischievous student erased?

Input

The first line of input contains a single integer $n$ ( $2 \le n \le 100$ ), which is the number of numbers that you wrote down.

The second line of input contains a string of digits, which represents the numbers you wrote down (minus the one that has been erased). There are no spaces in this string. It is guaranteed to contain all of the numbers from $1$ to $n$ , in order, except for the single number that the student erased.

Output

Output a single integer, which is the number that the tricky student erased.

Examples3

Example 1
Input
```
5
1235
```
Expected output
```
4
```
Example 2
Input
```
10
1234568910
```
Expected output
```
7
```
Example 3
Input
```
15
1234567891012131415
```
Expected output
```
11
```