#include<stdio.h>
long long int n,t,s,i,c[100001],p[100001],cm[100001],j,cost,sol;
int main()
{
	FILE *f,*g;
	f=fopen("branza.in","r");
	g=fopen("branza.out","w");
	fscanf(f,"%lld%lld%lld",&n,&s,&t);
	for(i=1;i<=n;i++)
	{ fscanf(f,"%lld%lld",&c[i],&p[i]);
	  cm[i]=c[i];
	}
	for(i=1;i<=n;i++)
	{ cost=(c[i]<cm[i])?c[i]:cm[i];
	  sol=sol+cm[i]*p[i];
	  for(j=1;j<=t;j++)
	  { if((j+i)>n)break;
	    if(c[i+j]<(c[i]+j*s))break;
	    if(cm[i+j]>(c[i]+j*s))cm[j+i]=c[i]+j*s;
	   }
	}
	fprintf(g,"%lld",sol);
	fcloseall();
	return 0;
}