*Time limit ：2000 ms
Memory limit ：262144 kB
Source ：Codeforces Beta Round #84 (Div. 2 Only)
Tags ：implementation 800
Editorial ：Announcement Tutorial
问题描述 ：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.
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”.**
#include <string>
#include <iostream>
using namespace std;
int main()
{
int len, j, a = 0;
char A[20];
cin >> A;
len = strlen(A);
for (j = 0; j < len; j++)
{
A[j] = A[j] - '0';
if (A[j]== 4|| A[j]==7)
a++;
}
if (a == 4||a==7)cout << "YES";
else cout << "NO";
return 0;
}