#include<stdio.h>
#include<algorithm>

using namespace std;

struct oaie
{
	int t,d,l;
};
oaie v[100000];
int n,l,x,max,i,j,tot,t[1000001];

bool cmp(oaie x, oaie y)
{
	if(x.t<y.t)return 1;
	if(x.t==y.t&&x.l>y.l)return 1;
	return 0;
}
int main()
{
	freopen("lupu.in","r",stdin);
	freopen("lupu.out","w",stdout);
	scanf("%d%d%d",&n,&x,&l);
	for(i=0;i<n;i++)
	{
		scanf("%d%d",&v[i].d,&v[i].l);
		v[i].t=(x-v[i].d)/l;
	}
	sort(v,v+n,cmp);
	i=0;
	while(i<n)
	{
		tot+=v[i].l;
		while(v[i].t==v[i+1].t)i++;i++;
	}
	printf("%d\n",tot);
	return 0;
}