It's and
, wants to know how many different numbers less than or equal to
that only consist of digits that are either
or
.
Subtasks
- (20 points)
- (80 points) No additional constraints.
Input Specification
A single integer
.
Output Specification
The answer to the problem, on a single line.
Sample Input 1
13
Sample Output 1
2
Explanation for Sample 1
The only two numbers are and
.
Sample Input 2
40
Sample Output 2
6
Explanation for Sample 2
The only valid numbers are ,
,
,
,
and
.
Comments
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You don't need to check every number. Consider the implications of the numbers only having the digits 2 and 3.