#include<stdio.h>

#define NMAX 100000
struct bee{int d,a,g;};
bee v[NMAX+1];

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