#include <stdio.h>
int min[100000],a[100000],b[100000],zi[100000];

int main()
{
    FILE *in,*out;
    int n,s,t,nr,rez=0,sum,i,j;
    in=fopen("branza.in","r");
    out=fopen("branza.out","w");
    fscanf(in,"%d%d%d",&n,&s,&t);
    for(i=0;i<n;i++)
    {
        fscanf(in,"%d%d",&a[i],&b[i]);
        nr=i+t;
        for(j=i;j<=nr;j++)
        {
            if((a[i]+s*(j-i)<min[j]&&min[i]!=0)||min[j]==0)
            {
                min[j]=a[i]+s*(j-i);
            }
        }
    }
    sum=0;
    for(i=0;i<n;i++)
    {
        rez+=min[i]*b[i];
    }
    fprintf(out,"%d",rez);
    return 0;
}