#include<iostream.h>
#include<stdio.h>
long long n,x,l,d[20000],a[20000],i,lana,ok=1,ord,aux;
int main()
{
	freopen("lupu.in","r",stdin);
	freopen("lupu.out","w",stdout);
	cin>>n>>x>>l;
	for(i=1;i<=n;i++)
		cin>>d[i]>>a[i];
	do
	{
		ord=1;
		for(i=1;i<n;i++)
			if(a[i]<a[i+1])
			{
				aux=a[i+1];
				a[i+1]=a[i];
				a[i]=aux;
				aux=d[i+1];
				d[i+1]=d[i];
				d[i]=aux;
				ord=0;
			}
	}while(ord==0);
	do
	{
		ok=1;
		for(i=1;i<=n;i++)
			if(d[i]<=x&&a[i]!=0) 
			{
				lana=lana+a[i];
				a[i]=0;
				ok=0;
				break;
			}
		for(i=1;i<=n;i++)
			d[i]=d[i]+l;
	}while(ok==0);
	cout<<lana;
}