Nearly Lucky Number

题面翻译

题目要求

如果一个数仅包含4和7，那么它就是一个"幸运数字"。 如果一个数本身不是幸运数，但是它所含有的数字4和7的个数之和为一个"幸运数字"，那么它就是一个"类幸运数字"。 给您一个数，请编程判断它是不是"类幸运数字"。

输入格式

一行一个整数N(N在64位整数(long long / int64)范围内)。

输出格式

一行一个字符串，如果N是"类幸运数字"则输出"YES"，否则输出"NO"。

感谢@PC_DOS 提供翻译

题目描述

Petya loves lucky numbers. We all know that lucky numbers are the positive integers whose decimal representations contain only the lucky digits 4 and 7. For example, numbers 47, 744, 4 are lucky and 5, 17, 467 are not.

Unfortunately, not all numbers are lucky. Petya calls a number nearly lucky if the number of lucky digits in it is a lucky number. He wonders whether number $n$ is a nearly lucky number.

输入格式

The only line contains an integer $n$ ( $1<=n<=10^{18}$ ).

Please do not use the %lld specificator to read or write 64-bit numbers in С++. It is preferred to use the cin, cout streams or the %I64d specificator.

输出格式

Print on the single line "YES" if $n$ is a nearly lucky number. Otherwise, print "NO" (without the quotes).

样例 #1

样例输入 #1

40047

样例输出 #1

NO

样例 #2

样例输入 #2

7747774

样例输出 #2

YES

样例 #3

样例输入 #3

1000000000000000000

样例输出 #3

NO

提示

In the first sample there are 3 lucky digits (first one and last two), so the answer is "NO".

In the second sample there are 7 lucky digits, 7 is lucky number, so the answer is "YES".

In the third sample there are no lucky digits, so the answer is "NO".