class Employee
{
public:
    int get_salary() const { return m_salary; }
    int get_balance() const { return m_balance; }
    void pay_salary() { m_balance += m_salary; }

    bool operator== (const Employee& rhs) const
    {
        return m_name == rhs.m_name &&
               m_age == rhs.m_age &&
               m_salary == rhs.m_salary &&
               m_balance == rhs.m_balance;
    }

private:
    std::string m_name;
    int         m_age;
    int         m_salary;
    int         m_balance;
};

int main()
{
    // ...
    auto employee_less_than = [] (const Employee& lhs, const Employee& rhs)
    		{
      			return lhs.get_balance() < rhs.get_balance();
    		};
    std::multiset<Employee, decltype(employee_less_than)> employees_sorted(employee_less_than);
    // ...
    int total_funds /* = ... */;
    for (auto& e : employees_sorted) {
        if (e.get_salary() <= total_funds) {
            total_funds -= e.get_salary();
            const_cast<Employee&>(e).pay_salary();
        }
    }
    // ...
}