#include <bits/stdc++.h>

using namespace std;
ifstream fin ("branza.in");
ofstream fout ("branza.out");
int main()
{
    int n,s,t;
    fin>>n>>s>>t;
    vector<int> cost(n);
    long long cost_total=0;
    t++;
    deque<int> dq;
    for (int i=0; i<n; i++)
    {
        int cantitate;
        fin>>cost[i]>>cantitate;
        if (!dq.empty() && dq.front()==i-t){
            dq.pop_front();
        }
        while (!dq.empty() && cost[i]<=cost[dq.back()]+(i-dq.back())*s){
            dq.pop_back();}
            dq.push_back(i);
            cost_total+=(long long)cantitate*(cost[dq.front()]+(i-dq.front())*s);
        }
        fout<<cost_total;

    return 0;
}