Ползуны

#include <iostream>
#include <conio.h>
#include <string>
#include <math.h>
#include <algorithm>
#include <set>
#include <map>

struct wheels
{
    int size;
    int pairwheel;
};
using namespace std;

int main()
{
    map <int, wheels> wheel;
    int n, prom;
    wheels prom2;
    prom2.size = 0;
    prom2.pairwheel = 1;
    set <int> size;

    cin >> n;
    for (int i = 1; i <= n; i++)
    {
        cin >> prom;
        if (wheel.find(prom) == wheel.end())
        {
            wheel.insert(pair <int, wheels>(prom, prom2));
        }
        else
        {
            wheel[prom].pairwheel = wheel[prom].pairwheel + 1;
            if (wheel[prom].pairwheel == 4)
            {
                wheel[prom].size = wheel[prom].size + 1;
                wheel[prom].pairwheel = 0;
            }
        }
        size.insert(prom);
    }

    int sum = 0;
    for (auto i = size.begin(); i != size.end(); i++)
    {
        sum = sum + wheel[*i].size;
    }

    cout << sum;

    _getch();
    return 0;
}