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Lucky Sevens

Easy · math

At the village fair, a raffle has printed a pile of tickets. You are given a list tickets of ticket numbers, each a whole number written in ordinary decimal digits (so 1707 is written 1, 7, 0, 7).

Seven is the lucky digit. Every 7 printed on a ticket brings the village one lucky point, so a ticket with two sevens brings two.

Return the total number of 7 digits printed across all the tickets. If the list is empty, return 0.

Examples

Example 1

Input: tickets = [7, 77, 1707]

Output: 5

The ticket 7 has one seven, 77 has two and 1707 has two, which makes 5.

Example 2

Input: tickets = [123, 456, 890]

Output: 0

Example 3

Input: tickets = [700000007, 0]

Output: 2

The first ticket has a seven at each end. The ticket 0 is written with a single digit, 0.

Constraints