Lucky Number

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Digits 4 and 7 are lucky, while all others are unlucky. An integer is lucky if it contains only lucky digits in decimal notation. We would like to know the K-th lucky positive integer. Input The first and only line of input contains a positive integer K (1 ≤ K ≤ 10^9). Output The first and only line of output must contain the K-th lucky positive integer. Example Input: 1 Output: 4 Input: 3

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solution.cppC++17

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