Problem Statement

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.

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.

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.

Sample Input 1

3 3 2
1 2
5 4
9 2

Sample Output 1

2

First, let us use a bomb at the coordinate 4 to decrease the first and second monsters' health by 2.
Then, use a bomb at the coordinate 6 to decrease the second and third monsters' health by 2.
Now, all the monsters' healths are 0.
We cannot make all the monsters' health drop to 0 or below with just one bomb.

Sample Input 2

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

Sample Output 2

5

We should use five bombs at the coordinate 5.

Sample Input 3

3 0 1
300000000 1000000000
100000000 1000000000
200000000 1000000000

Sample Output 3

3000000000

Watch out for overflow.

见题面 Input 部分

见题面 Output 部分