#include <iostream>

using namespace std;
struct deque1
{
    int s=4;
    int *arr1=new int[s];

    int index1st=0;
    int indexlast=s;
    int currentsize=0;

    void increasesize()
    {
        s*=2;
        int *arr2 = new int[s];
        for (int i = 0;i <= index1st;i++)
        {arr2[i]=arr1[i];}
        for (int i=s-1;i>=indexlast+(s/2);i--)
        {
            arr2[i]=arr1[i+s/2];
        }
        indexlast += s/2;
        arr2=arr1;
        delete[] arr1;

    }
    void pushback(int x)
    {

        currentsize++;
        if (currentsize>=s)
        {
            increasesize();
        }
        arr1[indexlast]=x;
        indexlast--;


    }
    void pushfront(int x)
    {
        currentsize++;
        if (currentsize>=s)
        {
            increasesize();
        }

        arr1[index1st]=x;
        index1st++;

    }
    int popfront()
    {
        if ((currentsize<=0))
        {
            return -1;
        }
        if (index1st<0)
        {
            index1st+=(s-1);
        }
        currentsize--;
        index1st--;
        return arr1[index1st];
    }
    int popback()
    {
        if ((currentsize<=0))
        {
            return -1;
        }
        if (indexlast>=s)
        {
            indexlast-=(s-1);
        }
        currentsize--;
        indexlast++;
        return arr1[indexlast];

    }


};

int main()
{
    int n;
    cin>>n;
    deque1 deque2;
    int command,number;
    int result;
    for (int i=0;i<n;i++)
    {cin>>command>>number;
        if (command==1)
        {
            deque2.pushfront(number);
        }
        if (command==2)
        {
            if (deque2.popfront()!= number)
            {cout<<"NO";
                break;}

        }
        if (command==3)
        {
            deque2.pushback(number);
        }
        if (command==4)
        {
            if (deque2.popback()!=number)
            {cout<<"NO";
                break;}}
        if (i==n-1)
        {
            cout<<"YES";
        }
    }
    return 0;
}