#include<stdio.h>
int n,i,j,a,b,v[10000],w[10000],x,l,max,ok,q=0;
FILE *f=fopen("lupu.in","r"),*g=fopen("lupu.out","w");
void main()
{
fscanf(f,"%ld %ld %ld",&n,&x,&l);
for(i=1;i<=n;i++)
{
fscanf(f,"%ld %ld",&a,&b);
if(a<=x)
{
j++;
v[j]=a;
w[j]=b;
}
}
n=j;
for(i=1;i<=n;i++)
{
max=0;
for(j=1;j<=n;j++)
{
if(w[j]>max&&v[j]<=x){max=w[j];ok=j;}
v[j]=v[j]+l;
}
q=q+max;
w[ok]=0;
}
fprintf(g,"%ld",q);
}