#include <iostream>
#include <fstream>
#include <deque>
using namespace std;
ifstream fin("branza.in");
ofstream fout("branza.out");
long long  n,s,t,c[100009],i,v;
long long sum;
deque <int> deq;
int main()
{
   fin>>n>>s>>t;
   fin>>c[1]>>v;
   sum+=v*c[1];
   deq.push_back(1);
   for(i=2;i<=n;i++){
    fin>>c[i]>>v;
    if(i-deq.front()==t+1)
        deq.pop_front();
    while(deq.empty()==0 && (c[deq.back()]+(i-deq.back())*s>=c[i]) )
        deq.pop_back();
    deq.push_back(i);
    sum+=(c[deq.front()]+(i-deq.front())*s)*v;
   }
   fout<<sum;

}