110A.Nearly_Lucky_Number.cpp

#include <bits/stdc++.h>
using namespace std;

int main()
{
    long long int n;
    int lucky = 0;

    cin >> n;

    while(n)
    {
        if(n % 10 == 7 || n % 10 == 4)
            lucky++;

        n = n / 10;
    }

    if(lucky == 7 || lucky == 4)
        cout <<"YES";
    else
        cout <<"NO";

    return 0;
}