110A - Nearly Lucky Number.cpp

/*
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 ?++. 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
inputCopy
40047
outputCopy
NO
inputCopy
7747774
outputCopy
YES
inputCopy
1000000000000000000
outputCopy
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<bits/stdc++.h>
using namespace std;

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    
   	long long n;
   	cin >> n;
   	
   	int lucky = 0;
   	
   	while (n) {
   		if(n % 10 == 4 || n % 10 == 7)
   			lucky++;
   		n /= 10;
	   }
	   
	if (lucky % 10 == 4 || lucky % 10 == 7)
		cout << "YES";
	else cout << "NO";

    return 0;
}