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 math
from bisect import bisect_right
N, D, A = map(int, input().split())  # N体のモンスター, 爆弾の範囲D, 爆弾の威力A
XH = []
X = []
for _ in range(N):
    x, h = map(int, input().split())
    XH.append((x, math.ceil(h/A)))  # 座標と必要な爆弾の個数を格納する
    X.append(x)  # こっちは座標のみ, あとで座標を二分探索するときに使う
# 座標でソートする
XH.sort()
X.sort()
T = [0]*(N+1)
now = 0
ans = 0
for i in range(N):
    x, h = XH[i]
    now -= T[i]
    if now >= h:
        continue
    else:
        T[bisect_right(X, x+D*2)] += h - now
        ans += h - now
        now = h
print(ans)