Masking credit card number

Given a number and an integer (n), return a new string as shown in the examples.

Sample Code:

function coverUp(num,n) {
// Enter your logic here...
}

Examples:

Input: 123456,3
Output: '***456'
Explanation: The first 3 numbers have been replaced by asterisk symbols.

Input: 12345678,4
Output: '****5678'
Explanation: The first 4 numbers have been replaced by asterisk symbols.