#include<fstream>
#include<queue>
using namespace std;
ifstream in("branza.in");
ofstream out("branza.out");
deque <int> d;
long long costa,cost;
int v[100001],cant,k;
int n ;
void stanga(int p)
{
    if(d.front()==p-k)
        d.pop_front();
}
void dreapta(int p)
{
    while(!d.empty() && (long long)v[p]*cant<=(long long)v[d.back()]*cant+(long long)cant*cost*(p-d.back() ) )
    {
        d.pop_back();
    }
    d.push_back(p);
}
int main()
{
    in>>n>>cost>>k;
    k++;
    for(int i=1;i<=n;i++)
    {
        in>>v[i]>>cant;
        stanga(i);
        dreapta(i);
        if(d.front()==i)
            costa=costa+(long long)v[i]*cant;
        else
            costa=costa+(long long)v[d.front()]*cant+(long long)cant*cost*(i-d.front());
    }
    out<<costa;
}