#include <fstream>
#include <deque>

using namespace std;

const int N = 100000;

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

int v[N];
long long c[N], p[N];
deque <int> dq;

int main()
{
    int n, s, t;
    cin >> n >> s >> t;
    t++;
    long long total = 0;
    for (int i = 0; i < n; i++)
    {
        int p;
        cin >> 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);

        total += (long long)p * ( c[dq.front()] + s * (i - dq.front()));
    }
    cout << total;
    return 0;
}