Codeforces - 110A

#include <bits/stdc++.h>

using namespace std;

int main()
{
    int count = 0;
    string number;
    cin >> number;
    for (int i = 0 ; i < number.size() ; i++){
        if (number[i] == '4' || number[i] == '7'){
            count++;
        }
    }
    if (count == 4 || count == 7){
        cout << "YES";
    }
    else
    cout << "NO";
    return 0;
}