We say that a number is **almost increasing** if for each digit of that number, either that digit is 0 or all digits to the left of it are (strictly) smaller than it. How many 4 digit numbers are almost increasing?

**Details and assumptions**

As an explicit example, the number $2035$ is almost increasing.

The number $12=012$ is a 2 digit number, not a 3 digit number.

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