#022 · Nearly Lucky Number · strings · medium · python
Petya loves lucky numbers. We all know that lucky numbers are the positive integers whose decimal
representations contain only the lucky digits 4 and 7.
For Example numbers: 47, 477, 4 are lucky and 5, 17, 467 are not.
Unfortunately, not all numbers are lucky. Petya calls a number nearly lucky if the number of
lucky digits in it is a lucky number.
Input:
the only line contains an integer n (1 Because Count of lucky number in 400447 is a lucky number also (4)!
### Example Input:
7747774
### Example Output:
YES
### Example Input:
1000000000000000000000000000
### Example Output:
NO