Nearly Luncky Number

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.

Input
The only line contains an integer n (1 ≤ n ≤ 1018).

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.

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

Examples
Input
40047
Output
NO
Input
7747774
Output
YES
Input
1000000000000000000
Output
NO
Note
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".
问题来源：https://vjudge.net/problem/CodeForces-110A
题目分析：是个坑，不仅要数字是4或7，还要位数也要是4位或者7位。
代码分析：对整数除10求余，如果余数为4或7 则位数+1，否则不加。如果位数是4位或者7位，则输出yes 否则 为no

#include
using namespace std;
int main()
{
    long long  s;
    cin >> s;
    int c = 0, i;
    while (s)
    {
        i = s % 10;
        if ((i== 7) || (i== 4))  c++;
        s = s / 10;
    }
    if (c == 7 || c == 4) cout << "YES" << endl;
    else cout << "NO" << endl;
    return 0;
}