#include <iostream>
#include <fstream>
#include <deque>

using namespace std;

ifstream in("branza.in");
ofstream out("branza.out");

long long v[100005];
deque <long long> d;
long long sum;

int main()
{
    long long n,s,t;
    in>>n>>s>>t;
    for(int i=0;i<n;i++)
    {
        in>>v[i];
        long long cant;
        in>>cant;
        if(!d.empty() && d.front()==i-t)
            d.pop_front();
        //bool conditie= (v[d.back()]+10*(i-d.back() ))*cant<=v[i]*cant;
        while(!d.empty() && v[d.back()]+s*(i-d.back() )>=v[i])
            d.pop_back();
        d.push_back(i);
        sum+=(v[d.front()]+s*(i-d.front() ))*cant;
    }
    out<<sum;
    return 0;
}