Hdu 1719 Friend

Friend

Time Limit: 1000/1000 MS (Java/Others) Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 2678 Accepted Submission(s): 1389

Problem Description

Friend number are defined recursively as follows.
(1) numbers 1 and 2 are friend number;
(2) if a and b are friend numbers, so is ab+a+b;
(3) only the numbers defined in (1) and (2) are friend number.
Now your task is to judge whether an integer is a friend number.

Input

There are several lines in input, each line has a nunnegative integer a, 0<=a<=2^30.

Output

For the number a on each line of the input, if a is a friend number, output “YES!”, otherwise output “NO!”.

Sample Input

13121

12131

Sample Output

YES!

NO!

#include <stdio.h>        
    int main()  
    {  
        __int64 n;  
        while(~scanf("%I64d",&n))  
        {  
            if(!n)  
            {  
                printf("NO!
");  
                continue;  
            }  
            n++;  
            while(n%2==0)  
                n/=2;  
            while(n%3 == 0)  
                n/=3;  
            if(n==1)  
                printf("YES!
");  
            else  
                printf("NO!
");  
        }  
      
        return 0;  
    }