#include <fstream>
#include <vector>
#include <deque>

using namespace std;

int main()
{
    ifstream in("branza.in");
    ofstream out("branza.out");
    int n, s, k;
    in >> n >> s >> k;
    k++;
    vector <int> pret(n);
    deque <int> dq;
    long long cost_total = 0;
    for (int i = 0; i < n; i++)
    {
        int c_i;
        in >> pret[i] >> c_i;
        while (!dq.empty() && pret[i] <= pret[dq.back()] + s * (i - dq.back()))
        {
            dq.pop_back();
        }
        dq.push_back(i);
        if (dq.front() == i - k)
        {
            dq.pop_front();
        }
        cost_total += (long long)c_i * (pret[dq.front()] + s * (i - dq.front()));
    }
    out << cost_total << "\n";
    in.close();
    out.close();
    return 0;
}