#include<bits/stdc++.h>
using namespace std;
long long c[200006]={0},d,n,j,k,i,l,t=0,ma=0;
struct bian{
	long long x,h;
}b[200006];
bool cmp(bian a,bian b)
{
	return a.x<b.x;
}

int main()
{
	scanf("%lld%lld%lld",&n,&d,&j);
	d=d*2;
	for(i=1;i<=n;i++)
	{
		scanf("%lld%lld",&b[i].x,&b[i].h);
		b[i].h=(b[i].h+j-1)/j;
	}
	sort(b +1,b+n+1 ,cmp);
	queue<long long> q;
	map<long long , long long> m;
	for(i=1;i<=n;i++)
	{
		if(t)
		while(!q.empty())
	    {
	    	if(q.front()<b[i].x)
	    	{
				t-=m[q.front()];
				q.pop();
			}
			else break;
		    
	    }
	    		if(t<b[i].h)
	    		{
					ma+=b[i].h-t;	
					q.push(b[i].x+d);
					m[b[i].x+d]=b[i].h-t;
					t=b[i].h;
					
				}
			
	}
	printf("%lld",ma);

}