4and7

#include <bits/stdc++.h>

using namespace std;

int numDigits(int number)
{
    int digits = 0;
    if (number < 0) digits = 1; // remove this line if '-' counts as a digit
    while (number) {
        number /= 10;
        digits++;
    }
    return digits;
}

int main() {
    int n;
    vector<int> passed;
    cin >> n;
    for(int a0 = 0; a0 < n; a0++){
        string name;
        int value;
        cin >> name >> value;
        vector<int> digits;
        while (value)
        {
            digits.push_back(value%10);
            value /= 10;        
        }
        int sz = digits.size();
        if (sz%2 != 0)
            cout << -1 << endl;
        else
        {
            int fours = 0;
            int sevens = 0;
            for (int i = 0; i < sz; i++)
            {
                if ((digits[i] != 4) || (digits[i] != 7))
                {
                    cout << -1 << endl;
                    break;
                }
                if (digits[i] == 4)
                    fours++;
                if (digits[i] == 7)
                    sevens++;
                
            }
            if (fours == sevens)
                
        }
        
        
    }
    return 0;
}