Is It a Lucky Number?
Alex loves lucky numbers. Help him find out if the given number n is lucky, return YES if its lucky and NO in the opposite case. Lucky numbers are positive integers that contain only the digits 4 and 7 in their decimal representation.
For example, numbers like 47, 744, and 4 are lucky, while numbers like 5, 17, and 467 are not.
Example 1
Input:
47
Output:
YES
Example 2
Input:
5
Output:
NO
main.cpp
C++
Demandez à l'IA
Demandez à l'IA
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