#153 67 sequence 1

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#153 67 sequence 1

Time limit: 1000 ms
Memory limit: 1024 MB
Checker: DIFF
Solve threshold: 100

Statement

Statement language

A string $S$ of length $N$ is given. $S$ consists only of the characters $0, 1, \cdots, 9$ . In one operation, you can choose and delete one character from the string. You want to perform given operation any number of times so that the character $6$ and the character $7$ never appear in the string. Find the minimum number of operations required.

Input

The input is given in the following format.

$N$ $S$

Output

Print the minimum number of operations required to make $6$ and $7$ never appear in the string.

Constraints

$1 \le N \le 300\,000$ .
$S$ is a string of length $N$ consisting only of the characters $0,1,\cdots,9$ .

Subtasks

#	Score	Constraints
1	15	$1 \le N \le 20$ .
2	40	$1 \le N \le 5\,000$ .
3	45	No additional constraints.

Samples

Sample 1

Input

10
1234567890

Output

Sample 2

Input

8
01234589

Output

Sample 3

Input

7
6677776

Output

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