countRoomsForTwo

George has recently entered the BSUCP (Berland State University for Cool Programmers). George has a friend Alex who has also entered the university. Now they are moving into a dormitory. 

George and Alex want to live in the same room. The dormitory has n rooms in total. At the moment the i-th room has pi people living in it and the room can accommodate qi people in total (pi ≤ qi). Your task is to count how many rooms has free place for both George and Alex.

Input

The first line contains a single integer n (1 ≤ n ≤ 100) — the number of rooms.

The i-th of the next n lines contains two integers pi and qi (0 ≤ pi ≤ qi ≤ 100) — the number of people who already live in the i-th room and the room's capacity.

Output

Print a single integer — the number of rooms where George and Alex can move in.

Examples

Input

3
1 1
2 2
3 3


Output

0


Input

3
1 10
0 10
10 10


Output

2

Function Signature

def countRoomsForTwo (rooms: List (Nat × Nat)) : Nat

Theorem Signature

def hasSpaceForTwo (room: Nat × Nat) : Bool :=
  let (current, capacity) := room
  capacity - current ≥ 2

def countRoomsForTwo_prop (rooms: List (Nat × Nat)) (out: Nat) : Prop := 
  out = (rooms.filter hasSpaceForTwo).length
theorem countRoomsForTwo_spec (rooms: List (Nat × Nat)) : countRoomsForTwo_prop rooms (countRoomsForTwo rooms)

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