/******************************************************************************

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*******************************************************************************/
#include <iostream>
#include <fstream>
#include <vector>
#include <deque>
using namespace std;
int n,s,t;
vector<pair<int,int>> v;
deque<int> dq;
int main()
{
    ifstream f("branza.in");
    ofstream g("branza.out");
    f>>n>>s>>t;
    for(int i=1; i<=n; i++)
    {
        int x,y;
        f>>x>>y;
        v.push_back({x,y});
    }
    int sum=0;
    int chir=s;
    for(int i=0; i<n; i++)
    {
        if(!dq.empty() && v[dq.back()].first+chir<v[i].first && i-dq.back()<=t)
        {
            sum+=(v[dq.back()].first+chir)*v[i].second;
            chir+=s;
        }
        else
        {
            sum+=v[i].first*v[i].second;
            dq.push_back(i);
            chir=s;
        }
        if (dq.front() <= i - t)
        {
            dq.pop_front();
        }
        //cout<<sum<<" "<<v[dq.back()].first<<endl;
    }
    g<<sum;

    return 0;
}