#include<stdio.h>
FILE *f=fopen("branza.in","r");
FILE *g=fopen("branza.out","w");
long long i,j,m[100001],n,t,s,rez;
long long c[100001],w[1000001];
long long deque[100001],u,p;

int main(){
//***citire***//	
fscanf(f,"%lld%lld%lld",&n,&s,&t);
for(i=1;i<=n;i++)
	fscanf(f,"%lld%lld",&c[i],&w[i]);

//***dinamica***//
p=1;
for(i=1;i<=n;i++)  // m[i]=costul minim pt a cumpara un kg de branza in ziua i
{ j=i-t;
  deque[i]=c[i];
  while(p<i&&( i-p>t || deque[p]+(i-p)*s > deque[i] ) )
	  p++;
  m[i]=deque[p]+(i-p)*s;
}
for(i=1;i<=n;i++)
	rez+=m[i]*w[i];
fprintf(g,"%lld",rez);
return 0;
}