#include <iostream>
using namespace std;
class deque
{
    int buffersize = 4;
    int* buffer;
    int back = 2;
    int front = 1;
    int amount = 0;
public:
    void grow ()
    {
        if (back == buffersize - 1)
            grow_back ();
        if (front == 0)
            grow_front ();
    }
    void grow_back ()
    {
        /*
        int newbuffersize = buffersize * 2;
        int* newBuffer = new int [newbuffersize];
        for (int i = 0; i < buffersize; i++)
            newBuffer [i] = buffer [i];
        delete[] buffer;
        buffersize = newbuffersize;
        buffer = newBuffer;
         */
        buffersize *= 2;
    }
    void grow_front ()
    {
        /*
        int newbuffersize = buffersize * 2;
        int* newBuffer = new int [newbuffersize];
        for (int i = newbuffersize / 2; i < newbuffersize ; i++)
            newBuffer [i] = buffer [i];
        front = buffersize;
        back += buffersize;
        delete[] buffer;
        buffersize = newbuffersize;
        buffer = newBuffer;
         */
        int reserve = buffersize;
        buffersize *= 2;
        for (int i = 0; i < reserve; i++)
            buffer [i + reserve] = buffer [i];
        front += reserve;
        back += reserve;
    }
    void push_back (int a)
    {
        grow ();
        buffer [back] = a;
        back++;
        amount++;
    }
    void push_front (int a)
    {
        grow ();
        buffer [front] = a;
        front--;
        amount++;
    }
    void pop_back ()
    {
        back--;
        amount--;
    }
    void pop_front ()
    {
        front++;
        amount--;
    }
    int elem_back ()
    {
        return buffer [back - 1];
    }
    int elem_front ()
    {
        return buffer [front + 1];
    }
    int count ()
    {
        return amount;
    }
};
int main ()
{
    int n = 0;
    cin >> n;
    deque arr;
    string truth = "YES";
    for (int i = 0; i < n; i++)
    {
        int a = 0;
        int b = 0;
        cin >> a >> b;
        if (a == 1)
            arr.push_front (b);
        if (a == 2)
        {
            if (b != arr.elem_front () or (arr.count () == 0 and b != -1))
                truth = "NO";
            else
                arr.pop_front ();
        }
        if (a == 3)
            arr.push_back (b);
        if (a == 4)
        {
            if (b != arr.elem_back () or (arr.count () == 0 and b != -1))
                truth = "NO";
            else
                arr.pop_back ();
        }
    }
    cout << truth << "\n";
    return 0;
}