An offer has been given. Determine if it contains the letter "
a" (English). If the answer is yes, output the serial number of the first of them. If it is negative, output the word 
NO.
Solve the problem 
 without using the built-in string functions, except for a function that returns the length of a string.
Input: The first line is the original sentence.
Output: print the answer to the problem.
Input and output example
| Test number | 
Input | 
Output | 
| 1 | 
foresete | 
NO | 
| 2 | 
forast | 
4 | 
  Запрещенные операторы:count;find