#include<stdio.h>



int main()
{
	long  n,S,T,cost[100000],cant[100000],m[100000],i,j,costa;
	long long total;
	FILE *f=fopen("branza.in","r");
	

	fscanf(f,"%i",&n);
	fscanf(f,"%i",&S);
	fscanf(f,"%i",&T);


	for(i=0;i<n;i++)
	{
		
		fscanf(f,"%i",cost+i);
		fscanf(f,"%i",cant+i);
		m[i]=32000;
	}




	for(i=0;i<n;i++)
	{
		for(j=0;j<=i;j++)
			if(i-j<=T) 
			{
			costa=cost[j]+((i-j)*S);
			if(costa<m[i]) m[i]=costa;
			}
	}


   
   for(i=0;i<n;i++)
	   total+=cant[i]*m[i];

   fclose(f);
   f=fopen("branza.out","w");

   fprintf(f,"%i",total);
   fclose(f);
   return 0;
}