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.

The input is given in the following format.

$N$ $S$

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

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