#include <fstream>
#include <deque>
using namespace std;
ifstream cin("branza.in");
ofstream cout("branza.out");
long long n,s,t;
long long cost[100005],sol;
deque<long long>d;
int main()
{
    cin>>n>>s>>t;
    d.push_back(1);
    for(int i=1;i<=n;i++)
    {
        int cantitate;
        cin>>cost[i]>>cantitate;

        while(!d.empty() && cost[i]-i*s<cost[d.back()]-d.back()*s)
            d.pop_back();

        d.push_back(i);

        sol+=cantitate*((i-d.front())*s+cost[d.front()]);

        if(i-d.front()==t)
            d.pop_front();
    }
    cout<<sol;
    return 0;
}
///trebuie sa calculam pretul minim cu care putem obtine 1 kg pe care sa-l dam in ziua i