taxi.cpp

#include <iostream>

int taxi(int one, int two, int three, int four)
{
    int cars = 0;
    cars = four;
    if((three - one) != 0)
    {
        cars += three - one;
        three = (three % one);
    }
    else
    {
        cars += three;
        one = one - three;
    }

    if(one > 1){
        if((two - one/2) != 0)
        {
            cars += two - one/2;
            two = two % one/2;
        }
        else
        {
            cars += two;
        }
        one = two;
    }
    else
    {
  cars += two / 2;
  two = two % 2;
  cars += two;
 
        cars += one;
    }
 return cars;

}

int main()
{
    int n;
    int one=0, two=0, three=0, four=0;
    std::cin>>n;
    for(int i=0; i<n; i++)
    {
        int n;
        std::cin>>n;
        switch(n)
        {
            case 1:
                one++;
                break;
            case 2:
                two++;
                break;
            case 3:
                three++;
                break;
            case 4:
                four++;
            default:
                break;
        }
    }
  int carsNeed = 0;

   carsNeed = taxi(one,two,three,four);
   std::cout<<carsNeed<<std::endl;
}