#include<stdio.h>
#define NMAX 100//000

struct oaie{
int d,a,g,r;
};

oaie v[NMAX+1];

int main(){
int s=0,n,l,x,i,gmax,max[NMAX+1]={0};
freopen("lupu.in","r",stdin);
freopen("lupu.out","w",stdout);
scanf("%d %d %d",&n,&x,&l);
gmax=x/l+1;
for(i=0;i<n;i++)
	{
	scanf("%d %d",&v[i].d,&v[i].a);
	if(v[i].d>x) {v[i].g=gmax+1;
				  continue;}
	v[i].g=v[i].d/l+1;
	v[i].r=v[i].d%l;
	if(v[i].r==0) v[i].g-=1;
	}
for(i=0;i<n;i++)
	if(v[i].g<=gmax){
		if(max[v[i].g]<v[i].a) max[v[i].g]=v[i].a;
		}
for(i=0;i<=gmax;i++)
s=s+max[i];
printf("%d",s);
return 0;
}