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 <bits/stdc++.h>

#define SORT(v, n) sort(v, v+n);
#define VSORT(v) sort(v.begin(), v.end());
#define size_t unsigned long long
#define ll long long
#define rep(i,a) for(int i=0;i<(a);i++)
#define repr(i,a) for(int i=(int)(a)-1;i>=0;i--)
#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define FORR(i,a,b) for(int i=(int)(b)-1;i>=a;i--)
#define ALL(a) a.begin(), a.end()
using namespace std;
int si() { int x; scanf("%d", &x); return x; }
long long sl() { long long x; scanf("%lld", &x); return x; }
string ss() { string x; cin >> x; return x; }
void pi(int x) { printf("%d ", x); }
void pl(long long x) { printf("%lld ", x); }
void pd(double x) { printf("%.15f ", x); }
void ps(const string &s) { printf("%s ", s.c_str()); }
void br() { putchar('\n'); }

const ll MOD = 1e9 + 7;
const ll INF = 1e9 + 5;

struct mint {
    int n;
    mint(int n_ = 0) : n(n_) {}
};

mint operator+(mint a, mint b) { a.n += b.n; if (a.n >= MOD) a.n -= MOD; return a; }
mint operator-(mint a, mint b) { a.n -= b.n; if (a.n < 0) a.n += MOD; return a; }
mint operator*(mint a, mint b) { return (long long)a.n * b.n % MOD; }
mint &operator+=(mint &a, mint b) { return a = a + b; }
mint &operator-=(mint &a, mint b) { return a = a - b; }
mint &operator*=(mint &a, mint b) { return a = a * b; }

typedef pair<ll, ll> P;

const ll N = 2e5+5;
string s;
vector<P> v;
ll n,d,a,X,H,result,num[N];
vector<ll> b,c;
queue<P> q;

int main () {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  cin >> n >> d >> a;
  rep(i,n) {
    cin >> X >> H;
    v.push_back(P(X,H));
  }
  VSORT(v);
  rep(i,n) {
    b.push_back(v[i].second);
    c.push_back(v[i].first);
  }
  ll num = 0;
  rep(i,n) {
    while(q.size() > 0 && q.front().first < v[i].first) {
      num -= q.front().second;
      q.pop();
    }
    v[i].second -= num * a;
    if (v[i].second > 0 ){
      ll temp = (v[i].second-1) / a + 1;
      q.push(P(v[i].first + 2 * d, temp));
      num += temp;
      result += temp;
    }
    cout << i << " : " << num << endl;
  }
  cout << result << endl;
}