Problem:
Score : 200 points

Problem Statement

In a factory, there are N robots placed on a number line.
Robot i is placed at coordinate X_i and can extend its arms of length L_i in both directions, positive and negative.

We want to remove zero or more robots so that the movable ranges of arms of no two remaining robots intersect.
Here, for each i (1 \leq i \leq N), the movable range of arms of Robot i is the part of the number line between the coordinates X_i - L_i and X_i + L_i, excluding the endpoints.

Find the maximum number of robots that we can keep.

Constraints

1 \leq N \leq 100,000

0 \leq X_i \leq 10^9 (1 \leq i \leq N)

1 \leq L_i \leq 10^9 (1 \leq i \leq N)

If i \neq j, X_i \neq X_j.

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N
X_1 L_1
X_2 L_2
\vdots
X_N L_N

Output

Print the maximum number of robots that we can keep.

Sample Input 1

4
2 4
4 3
9 3
100 5

Sample Output 1

3

By removing Robot 2, we can keep the other three robots.

Sample Input 2

2
8 20
1 10

Sample Output 2

1

Sample Input 3

5
10 1
2 1
4 1
6 1
8 1

Sample Output 3

5

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

program ap
  implicit none
  integer :: ans, larg, cnttai,in
  integer :: h, w , n, i, sumers, csum, err, j, jc(1)
  integer,allocatable,dimension(:) :: X, xmax, xmin
  integer,allocatable,dimension(:) :: L, cnt,ers
    integer,allocatable,dimension(:,:) :: taio

  read(*,*) n

  allocate( X(n) )
  allocate( L(n) )
  allocate( xmax(n) )
  allocate( xmin(n) )
  allocate( cnt(n) )
  allocate( ers(n) )
  allocate( taio(n,n) )
  
  do i=1,n
     read(*,*) X(i), L(i)
     xmax(i)=X(i)+L(i)
     xmin(i)=X(i)-L(i)
  enddo

  ers(:)=0
  cnt(:)=0
  sumers=0
  csum=0
  taio(:,:)=0
  do i=1,n
     do j=1,n
        if(i.eq.j) goto 300
        w=0
        if(xmax(i).gt.xmin(j).and.xmax(i).le.xmax(j)) then
           w=w+1
        endif
        if(xmin(i).lt.xmax(j).and.xmin(i).ge.xmin(j)) then
           w=w+1
        endif
        
        
        if(w.eq.2) then
           ers(j)=1
!           cnt(j)=cnt(j)+1
           taio(j,i)=1
           print *, i, j
        elseif(w.eq.1) then
!           cnt(j)=cnt(j)+1
           taio(j,i)=1
        endif
        300 continue
     enddo
  enddo
  do j=1,n
     do i=1,n
        csum=csum+taio(j,i)
        !     sumers=sumers + ers(j)
     enddo
  enddo
  err=0

  do j=1,n
     if(ers(j).eq.1) then
        do i=1,n
           cnttai=cnttai+taio(j,i)
        enddo
        csum=csum-cnttai*2
        taio(j,:)=0
        taio(:,j)=0
        err=err+1
     endif
  enddo
!  print *, err  

  if(sum(taio).le.0) goto 400


  cnt(:)=0
  do j =1,n
     do i=1,n
        cnt(j)=cnt(j)+taio(j,i)
     enddo
  enddo
  
  do i=1,n

     cnt(:)=0
     do j =1,n
        do in=1,n
           cnt(j)=cnt(j)+taio(j,in)
        enddo
     enddo


     jc=maxloc(cnt)
     err=err+1
     cnt(jc(1))=0
     taio(jc(i),:)=0
     taio(:,jc(i))=0
     if(sum(taio).le.0) goto 400

  enddo
400 continue
  
  print *,  n-err
  
end program ap