Problem:
Score : 600 points

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.

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.

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.

Solution in C++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <algorithm>
#include <iostream>
#include <vector>
#include <map>
#include <cstdio>
#include <string>
#include <cmath>
#include <queue>
#include <tuple>
#include <set>
#include <assert.h>
#include <sstream>
#include <string>
//#include <bits/stdc++.h>
#define maxs(x,y) x = max(x,y)
#define mins(x,y) x = min(x,y)
#define rep(i,n) for(int (i)=0;(i)<(n);(i)++)
#define repr(i, n) for (int i = (n) - 1; i >= 0; i--)
#define FOR(i,i0,n) for(int (i)=(i0);(i)<(n);(i)++)
#define FORR(i,i0,n) for(int (i)=(n)-1; (i)>=(i0);(i)--)
#define SORT(x) sort(x.begin(),x.end())
#define SORTR(x) sort(x.begin(),x.end(),greater <>())
#define rn return
#define fi first
#define se second
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define mt make_tuple
using namespace std;
using ll = long long;
typedef std::pair<ll,ll> P;
//#include <boost/multiprecision/cpp_int.hpp>
//using bint = boost::multiprecision::cpp_int;



int main(){
    ll n,d,a;
    cin >> n >> d >> a;
    d *= 2;
    vector<P> xh(n);
    rep(i,n) cin >> xh[i].fi >> xh[i].se;
    queue<P> bombZone;
    SORT(xh);
    ll ans = 0;
    ll totalDamage = 0;
    rep(i,n){

        
        ll h = xh[i].se;
        ll x = xh[i].fi;
        while(bombZone.size() && bombZone.front().fi < x){
            totalDamage -= bombZone.front().se;
            bombZone.pop();
        }
        h -= totalDamage;
        
        if (h>0){
            ll count = (h+a-1)/a;
            ans += count;
            totalDamage += a*count;
            bombZone.push(mp(x+d,totalDamage));
        }
    }
    cout << ans;
    
    
}