#include <iostream>

using namespace std;
struct deque1
{
int s=128;
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;i>=indexlast;i--)
 {
     arr2[i]=arr1[i+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;
}
currentsize--;
index1st--;
return arr1[index1st];
}
int popback()
{
  if ((currentsize<=0))
  {
    return -1;
  }
 currentsize--;
 indexlast++;
 return arr1[indexlast];

 }
 void multipop()
 {
     cout << '\n' << "Dequeue: ";
     for (int i = 0; i < currentsize; i++)
     {
         cout << arr1[(index1st + i)%s] << " ";
     }
     cout << '\n';
 }
};

int main()
{
int n;
cin>>n;
deque1 deque2;
int Reading[2*n];
int Results[n];
for (int i=0;i<2*n;i++)
{cin>>Reading[i];
}
for (int i=0;i<2*n;i++)
{
    if (Reading[2*i]==1)
    {
        deque2.pushfront(Reading[2*n+1]);
    }
     if (Reading[2*i]==2)
    {
        if (deque2.popfront()!= Reading[2*i+1])
            {cout<<"NO";
            break;}

    }
     if (Reading[2*i]==3)
    {
       deque2.pushback(Reading[2*i+1]);
    }
     if (Reading[2*i]==4)
    {
       if (deque2.popback()!=Reading[2*i+1])
        {cout<<"NO";
        break;}

    }
    if (i==2*n-1)
    {
        cout<<"YES";
    }
deque2.multipop();

}


return 0;
}