PROGRAMMING:How many are seven?

###Description
Read in a 4-digit integer from the keyboard and find out how many digits are 7
###Input format:
A 4-digit integer
###Output format:
The number of 7 in the integer
###Input example:
Here is a set of inputs. For example:
```in
four thousand seven hundred and fifty-seven
```
###Output example:
The corresponding output is given here. For example:
```out
two
```







answer：If there is no answer, please comment