Problem:
Score : 200 points

Problem Statement

There are four towns, numbered 1,2,3 and 4.
Also, there are three roads. The i-th road connects different towns a_i and b_i bidirectionally.
No two roads connect the same pair of towns. Other than these roads, there is no way to travel between these towns, but any town can be reached from any other town using these roads.

Determine if we can visit all the towns by traversing each of the roads exactly once.

Constraints

1 \leq a_i,b_i \leq 4(1\leq i\leq 3)

a_i and b_i are different. (1\leq i\leq 3)

No two roads connect the same pair of towns.

Any town can be reached from any other town using the roads.

Input

Input is given from Standard Input in the following format:

a_1 b_1
a_2 b_2
a_3 b_3

Output

If we can visit all the towns by traversing each of the roads exactly once, print YES; otherwise, print NO.

Sample Input 1

4 2
1 3
2 3

Sample Output 1

YES

We can visit all the towns in the order 1,3,2,4.

Sample Input 2

3 2
2 4
1 2

Sample Output 2

NO

Sample Input 3

2 1
3 2
4 3

Sample Output 3

YES

Solution in Fortran (gfortran v4.8.4) (judge verdict: Accepted)

module Sort_Module
    implicit none
    public
    contains
    recursive subroutine mergesort(a, p, r, b)
        integer(8) a(:), b(:)
        integer(8) p, r
        integer(8) q
        if (p < r) then
            q = (p+r)/2
            call mergesort(a, p, q, b)
            call mergesort(a, q+1, r, b)
            call merge(a, p, q, r, b)
        end if
    end subroutine mergesort
    subroutine merge(a, p, q, r, b)
        integer(8) a(:), b(:)
        integer(8) p, r, q, i, j, k
        integer(8) t
        k = p;   i = p;   j = q+1
        do
            if (.not. (k <= r)) exit
            if (j > r) then
                t = a(i);   i = i+1
            else if (i > q) then
                t = a(j);   j = j+1
            else if (a(i) <= a(j)) then
                t = a(i);   i = i+1
            else
                t = a(j);   j = j+1
            end if
            b(k) = t;   k = k+1
        end do
        do i = p, r
            a(i) = b(i)  
        end do
    end subroutine merge
    subroutine sort(a)
      integer(8) a(:),b(ubound(a,1)-size(a)+1:ubound(a,1)),n,k
      n = ubound(a,1)
      k = ubound(a,1)-size(a)+1
      call mergesort(a,k,n,b)
    end subroutine sort
    function POSL(a,v) result(r)!find first i:a(i)>=v
        implicit none
        integer(8) :: a(:),l,r,idx,v
        r = ubound(a,1) + 1
        l = ubound(a,1)-size(a)
        do while(r-l>1)
            idx = l + (r-l)/2
            if(a(idx) >= v)then
                r = idx
            else
                l = idx
            endif
        enddo
    end function
    function POSU(a,v) result(r)!find first i:a(i)>v
        implicit none
        integer(8) :: a(:),l,r,idx,v
        r = ubound(a,1) + 1
        l = ubound(a,1)-size(a)
        do while(r-l>1)
            idx = l + (r-l)/2
            if(a(idx) > v)then
                r = idx
            else
                l = idx
            endif
        enddo
    end function
    function NUM(a,v) result(n)
        implicit none
        integer(8) :: a(:),v,n
        n = POSU(a,v) - POSL(a,v)
    end function
end module Sort_Module
  

program atcoder
    use Sort_Module
    implicit none
    integer(8) :: ans,a,b,c(1:4),i,d(1:4)
    c=0
    do i=1,3
        read*,a,b
        c(a)=c(a)+1
        c(b)=c(b)+1
    enddo
    call sort(c)
    d(1)=1
    d(2)=1
    d(3)=2
    d(4)=2
    if( all(d==c) )then
        write(*,'(a)')"YES"
    else 
        write(*,'(a)')"NO"
    endif
    stop 
contains
end program atcoder