PROGRAMMING:Judge perfect number
Program input a positive integer n not less than 6 (n < 9999999) and output whether it is a complete number. A number whose sum of true divisors is exactly equal to itself is a perfect number.
###Input example:
```in
twenty-eight
```
###Output example:
```out
YES
```
###Input example:
```in
one hundred
```
###Output example:
```out
NO
```
answer：If there is no answer, please comment
###Input example:
```in
twenty-eight
```
###Output example:
```out
YES
```
###Input example:
```in
one hundred
```
###Output example:
```out
NO
```
answer：If there is no answer, please comment