function solveClasses() {

    class Developer{
        constructor ( firstName, lastName ){
            this.firstName=firstName;
            this.lastName=lastName;
            this.baseSalary = Number(1000);
            this.tasks = [];
            this.experience = Number(0);

        }
        addTask ( id, taskName, priority ){
            let task = {id, name: taskName, priority}; //да внимавам дали е name или taskName
            if(priority == 'high'){
                this.tasks.unshift(task);
            }
            else{
                this.tasks.push(task);
            }
            return `Task id ${id}, with ${priority} priority, has been added.`;

        }

        doTask(){
            let task = this.tasks.find(x => x.priority == 'high');
            if(!task){
                return `${task.name}`;
            }
            return `${this.firstName}, you have finished all your tasks. You can rest now.`;
        }

        getSalary(){
            return `${this.firstName} ${this.lastName} has a salary of: ${this.baseSalary}`;
        }

        reviewTasks(){
            let output = `Tasks, that need to be completed:\n`;

            for (let task of this.tasks) {
                output += `${task.id}: ${task.name} - ${task.priority}\n`;
            }
            return output.trim();
        }
    }

    class Junior extends Developer{
        constructor( firstName, lastName, bonus, experience ){
            super(firstName,lastName);
            this.bonus = Number(bonus);
            this.baseSalary = Number(1000) + this.bonus;
            this.taskName = [];
            this.experience = Number(experience);
        }

        learn(years){
            this.experience +=years;
        }
    }

    class Senior extends Developer{
        constructor( firstName, lastName, bonus, experience ){
            super(firstName,lastName);
            this.bonus = Number(bonus);
            this.baseSalary = Number(1000) + this.bonus;
            this.tasks = [];
            this.experience = Number(experience) + Number(5);
        }

        changeTaskPriority(taskId){


            let task = this.tasks.find(x => x.id == taskId);
            this.tasks = this.tasks.filter(x => x.id != taskId); //всички задачи без конкретната

            if(task.priority == 'high'){
                task.priority = 'low';
                this.tasks.push(task);
            }
            else{
                task.priority = 'high';
                this.tasks.unshift(task);
            }
            return task;

        }

    }


    return {
        Developer,
        Junior,
        Senior
    }
}