string number_to_string(int x) {
    string s = "";
    while(x > 0) {
        s += (x % 10) + '0';
        x /= 10;
    }
    reverse(s.begin(), s.end());
    return s;
}

int string_to_number(string &s) {
    int number = 0;
    for(int i = 0; i < s.size(); i++) {
        number = (number * 10) + (s[i] - '0');
    }
    return number;
}