#include <fstream>
#include <deque>

using namespace std;

ifstream in ("branza.in");
ofstream out ("branza.out");

const int N = 100000;

int c[N];

deque <int> dq;

int main()
{
    int n, s, t, p;
    long long cost = 0;
    in >> n >> s >> t;
    for (int i = 0; i < n; i++)
    {
        in >> c[i] >> p;
        if (!dq.empty() && dq.front() == i - t)
        {
            dq.pop_front();
        }
        while (!dq.empty() && c[i] <= c[dq.back()] + s * (i - dq.back()))
        {
            dq.pop_back();
        }
        dq.push_back(i);
        if (i >= t - 1)
        {
            cost += (c[dq.back()] + s * (i - dq.front())) * (long long) p;
        }
    }
    out << cost;
    return 0;
}