PROGRAMMING:Password strength

This topic requires according to the input password string (string length greater than 6), output password strength. Rule: the password can only contain uppercase letters, lowercase letters, numbers and underscores. If only one of them is included, the password strength is 1; If two of them are included, the password strength is 2; If three of them are included, the password strength is 3; If four of them are included, the password strength is 4.
###Input format:
Enter a string with a length greater than 6.
###Output format:
Output password strength.
###Input sample 1:
Here is a set of inputs. For example:
```in
one hundred and twenty-three million four hundred and fifty-six thousand seven hundred and eighty-nine
```
###Output sample 1:
The corresponding output is given here. For example:
```out
one
```
###Input sample 2:
Here is a set of inputs. For example:
```in
abcd666
```
###Output sample 2:
The corresponding output is given here. For example:
```out
two
```
###Input sample 3:
Here is a set of inputs. For example:
```in
aBCD666
```
###Output sample 3:
The corresponding output is given here. For example:
```out
three
```
###Input sample 4:
Here is a set of inputs. For example:
```in
aBCD_ six hundred and sixty-six
```
###Output sample 4:
The corresponding output is given here. For example:
```out
four
```






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