#include<stdio.h>
struct branza{long long s,i;}a[100500];
long long n,s,t,st,dr,i;
long long cc,ca,ss,S;
int main()
{
 freopen("branza.in","r",stdin);
 freopen("branza.out","w",stdout);
 scanf("%lld%lld%lld",&n,&s,&t);
 st=1;
 dr=0;
 for(i=1;i<=n;++i)
    {scanf("%lld%lld",&cc,&ca);
     ss=cc+(n-i)*s;
     while(dr&&a[dr].s>ss)--dr;
     a[++dr].s=ss;
     a[dr].i=i;
     while(a[st].i<=i-t&&st<=dr)++st;
     ss=a[st].s;
     ss-=((n-i)*s);
     S+=(ss*ca);}
 printf("%lld\n",S);
 return 0;
}