#include <bits/stdc++.h>
using namespace std;
long long n,d,b,j,k[200005],k2[200005],w,sum,ans,sum1[200005],ii;
pair <long long, long long> a[200005];
int main()
{
	cin>>n>>d>>b;
	for (int i=1; i<=n; i++)
	{
		cin>>a[i].first>>a[i].second;
	}
	sort(a+1, a+n+1);
	j=1;
	for (int i=1; i<=n;i++)
	{
		
			while(k[j]<a[i].first  && j<=ii)
		{
			sum-=sum1[j];
			j++;
		} 
		
		a[i].second-=sum;  
		if(a[i].second>0){
		ii++;
		k[ii]=a[i].first+2*d; 
		if (a[i].second%b==0)
		{
			w=a[i].second/b;
		}
		else
		w=a[i].second/b+1;
		sum+=w*b;
		sum1[ii]=w*b;
	ans+=w; 
	} }
	cout<<ans<<endl;
}