PROGRAMMING:Nested loop prime number

Input two positive integers a and B, and then output the number of primes between them (excluding a and b).
###Input format:
Enter positive integers a and B, separated by spaces.
###Output format:
Output the number of prime numbers between two numbers (excluding these two numbers). If the input is negative, there is no output.
###Input example:
Here is a set of inputs. For example:
```in
10 20
```
###Output example:
The corresponding output is given here. For example:
```out
four
```







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