#import<bits/stdc++.h>
using namespace std;
typedef long long LL;
typedef struct{LL x;LL h;}H;
LL a,d,h,i,j,k,m,n,s,t,z[200040];
H w[200040];
int C(H a,H b){return a.x<b.x;}
int main()
{
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
	cout.tie(NULL);
	cin>>n>>d>>a;
	for(;i<n;i++)cin>>w[i].x>>w[i].h;
	sort(w,w+n,C);
	w[n].x=w[n].h=4000000000;
	d*=2;
	for(i=0;j<n;)
	{
		if(w[j].x-w[i].x>d)t-=z[i++];
		else
		{
			if(w[j].h>t)
			{
				m=(w[j].h-t-1)/a+1;
				s+=m;
				m*=a;
				z[j]=m;
				t+=m;
			}
			
			j++;
		}
	}
	cout<<s;
}