Problem: Silver Fox is fighting with N monsters.

The monsters are standing in a row, and we can assume them to be standing on a number line. The i-th monster, standing at the coordinate X_i, has the health of H_i.

Silver Fox can use bombs to attack the monsters. Using a bomb at the coordinate x decreases the healths of all monsters between the coordinates x-D and x+D (inclusive) by A. There is no way other than bombs to decrease the monster's health.

Silver Fox wins when all the monsters' healths become 0 or below.

Find the minimum number of bombs needed to win.

Constraints

* 1 \leq N \leq 2 \times 10^5
* 0 \leq D \leq 10^9
* 1 \leq A \leq 10^9
* 0 \leq X_i \leq 10^9
* 1 \leq H_i \leq 10^9
* X_i are distinct.
* All values in input are integers.

Input

Input is given from Standard Input in the following format:


N D A
X_1 H_1
:
X_N H_N


Output

Print the minimum number of bombs needed to win.

Examples

Input

3 3 2
1 2
5 4
9 2


Output

2


Input

9 4 1
1 5
2 4
3 3
4 2
5 1
6 2
7 3
8 4
9 5


Output

5


Input

3 0 1
300000000 1000000000
100000000 1000000000
200000000 1000000000


Output

3000000000

Solution (in PYTHON3):

Solution:
import sys
input = sys.stdin.readline

from heapq import heappush, heappop

N, D, A = map(int, input().split())
XH = [[int(i) for i in input().split()] for _ in range(N)]

XH.sort()

ret = 0
hp = []
s = 0
for i, (x, h) in enumerate(XH) :
  while len(hp) > 0 and hp[0][0] < x - D :
    s -= heappop(hp)[1]
    
  if s > h :
    continue
  
  cnt = (h - s + A - 1) // A
  ret += cnt
  heappush(hp, (x + D, cnt * A))
  s += cnt * A

print(ret)