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: Time Limit Exceeded)

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define _overload3(_1,_2,_3,name,...) name
#define _rep(i,n) repi(i,0,n)
#define repi(i,a,b) for(ll i=ll(a);i<ll(b);++i)
#define rep(...) _overload3(__VA_ARGS__,repi,_rep,)(__VA_ARGS__)
#define inf (ll)1e9
#define mod (ll)(1e9+7)
#define d(x) cerr<<#x<<"="<<x<<endl;
#define p(x) cout<<(x)<<endl
#define ps(x) cout<<(x);
#define pk(x) cout<<(x)<<" ";
#define pfix(d,x) cout << fixed << setprecision(d) << x << endl;
#define pb push_back
#define all(v) (v).begin(), (v).end()
#define minel(v) *min_element(all(v))
#define minind(v) distance((v).begin(), min_element(all(v)))
#define maxel(v) *max_element(all(v))
#define maxind(v) distance((v).begin(), max_element(all(v)))
#define p2d(v,n,m) rep(i,n){rep(j,m){pk(v[i][j]);}p("");}
#define fi first
#define se second
template<typename A, size_t N, typename T>
void Fill(A (&array)[N], const T &val){
    std::fill( (T*)array, (T*)(array+N), val );
}
ll a[100001],b[100001],c[100001],d,n,m,x,y,z,h,w,k,sum,mi=inf,ma=-inf,ans,s,t,l,r,res,tmp,itr,p,q;
bool flag;
int dx[4]={1,0,-1,0},dy[4]={0,1,0,-1};
int dx8[8]={1,1,0,-1,-1,-1,0,1},dy8[8]={0,1,1,1,0,-1,-1,-1};
char cha;
string st;
typedef map<ll, ll> imap;
typedef pair<ll, ll> P;
typedef vector<int> VI;
typedef vector<ll> VL;
typedef vector<pair<ll,ll> > VP;
P pa;

ll damages[200002];

int main(){
    cin>>n>>d>>m;
    VP vp;
    rep(i,n){
        cin>>x>>h;
        vp.pb({x,h});
    }
    sort(all(vp));
    //尺取り法でx_iが左端の場合の攻撃範囲を求める
    ll bombnum,nowhp,damage;
    rep(i,n){
        rep(j,r+1,n){
            if(vp[j].fi-vp[i].fi<=2*d)r++;
        }
        //iからはrまで届く。
        nowhp=vp[i].se-damages[i];
        if(nowhp>0){
            bombnum=((nowhp%m)?nowhp/m+1:nowhp/m);
            sum+=bombnum;
            damage=bombnum*m;
            damages[i]+=damage;
            damages[r+1]-=damage;
        }
        damages[i+1]+=damages[i];
        //rep(i,n+1)d(damages[i]);
    }
    p(sum);
    return 0;
}