#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define lvector vector<ll> 
typedef pair<ll,ll> P;
#define rep(i,n) for(ll (i)=0; i<(n); ++(i))
#define print(a) cout << (a) << endl

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  ll n,d,a,x,h,bomb=0,tot=0,ans=0;cin>>n>>d>>a;d*=2;
  vector<P> v(n);
  rep(i,n) { cin>>x>>h; v[i]=P{x,(h+a-1)/a}; }
  sort(v.begin(),v.end());
  queue<P> q;
  rep(i,n) {
    while(q.size() && q.front().first<v[i].first) {
      tot-=q.front().second;
      q.pop();
    }
    v[i].second-=tot;
    if(v[i].second>0) {
      bomb=v[i].second;
      ans+=bomb;
      tot+=bomb;
      q.emplace(v[i].first+d,bomb);
    }
  }
  print(ans);
  return 0;
}