#include <bits/stdc++.h>
using namespace std;
typedef pair<int,int> pii;
int n,d,a,x,h,idx;long long diff,toadd,out=0;
vector<pii> vii;
vector<int>bombs;
vector<long long>sums;
int bsearch(int val)
{
    int b,e,mid,ans=-1;
    b=0,e=bombs.size()-1;

    while(b<=e)
    {
        mid=b+(e-b)/2;

        if(bombs[mid]==val)
        {
            ans=mid;
            return ans;
        }
        else if(bombs[mid]<val)
        {
            b=mid+1;
        }
        else
        {
            ans=mid;
            e=mid-1;
        }
    }
    return ans;
}
int main(){
   cin>>n>>d>>a;
   for(int i=0;i<n;i++)
   {
       cin>>x>>h;
       vii.push_back(make_pair(x,h));
   }
   sort(vii.begin(),vii.end());

   for(int i=0;i<n;i++)
   {
       x= vii[i].first;
       h= vii[i].second;
       idx = bsearch(x-2*d);
       if(idx>=0&&bombs[idx]>=x-2*d)
       {
           diff= sums[sums.size()-1]-(idx==0?0:sums[idx-1]);
           h-=(diff*a);
           if(h>0)
           {
               bombs.push_back(x);
               out += (long long)ceil(h/a);
               sums.push_back(out);
           }
       }
       else
       {
           bombs.push_back(x);
           out += (long long)ceil(h/a);
           sums.push_back(out);
       }
   }
   cout<<out<<endl;
	return 0;
}
