#include<stdio.h>
#define maxn 100003
long n,i;
long long v[maxn],x,l,a,d,s;
FILE *f, *g;
int main()
{f=fopen("lupu.in","r");
g=fopen("lupu.out","w");
fscanf(f,"%ld %lld %lld",&n,&x,&l);
for(i=1;i<=n;i++)
{fscanf(f,"%lld %lld",&d,&a);
if(d<=a &&v[(x-d)/l+1]<a)
v[(x-d)/l+1]=a;}
for(i=1;i<=n;i++)
s+=v[i];
fprintf(g,"%lld",s);
fclose(f);
fclose(g);
return 0;}