#include <iostream>
#include <deque>
#include <fstream>
using namespace std;

deque<int>v;
long long c[100000],p[100000],sum=0;
int main()
{
    int n,s,t,i;
    //std::deque<int>::iterator it;
    ifstream f("branza.in");
    ofstream g("branza.out");
    f>>n>>s>>t;
    t++;
    for(i=0; i<n; i++)
        f>>c[i]>>p[i];
    for(i=0; i<n; i++)
    {
        //it=v.begin();
        if(!v.empty() && i-*v.begin()==t)
            v.pop_front();
        //it=v.end();
        while(!v.empty() && c[i]<=c[*v.end()]+s*(i-*v.end()))
        {
            v.pop_back();
            //it=v.end();
        }

        v.push_back(i);
        //it=v.begin();
        sum=sum+p[i]*(c[*v.begin()]+s*(i-*v.begin()));
    }
    g<<sum;
    return 0;
}