p02788 AtCoder Beginner Contest 153 - Silver Fox vs Monster
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
```python
from math import * 
import sys
input = sys.stdin.readline

def main():
    N, D, A = list(map(int, input().split()))
    XH = sorted([list(map(int, input().split())) for i in range(N)])

    t = 0
    q = []
    ans = 0
    for X, H in XH:
        while q and q[0][0] < X-D:
            x, c = q.pop(0)
            t -= c
        H -= A * t
        
        if H <= 0: continue 

        c = ceil(H/A)
        ans += c
        q.append((X+D, c))
        t += c   
    print(ans)
if __name__ == '__main__':
    main()

```