#include <stdio.h>
#define Dim 100010
long long c[Dim],p[Dim],d[Dim],n,s,t,in=1,sf=1,i;
struct deque {
	int element,valoare;
} dq[Dim];
int main()
{
	freopen("branza.in","r",stdin);
	freopen("branza.out","w",stdout);
	scanf("%d%d%d",&n,&s,&t);
	for (i=1;i<=n;i++) 
	{
		scanf("%d%d",&c[i],&p[i]);
	}
	d[1]=c[1];
	dq[1].valoare=c[1]+(n-1)*s;
	dq[1].element=1;
	for(i=1;i<=n;i++) 
	{
		while(i-dq[in].element>t) in++;
		while(sf>=in && (c[i]+(n-i)*s<dq[sf].valoare)) sf --;
		dq[++sf].valoare=c[i]+(n-i)*s;
		dq[sf].element=i;
		d[i]=dq[in].valoare-(n-i)*s;
	}
    long long rez=0;
	for(i=1;i<=n;i++) 
	{
		rez+=p[i]*d[i];
	}
	printf("%d\n",rez);
	return 0;
}