#include <fstream>
#include <deque>

using namespace std;

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

int n, s, t, ans;

struct week {
    int pos, cost;
};

deque <week> v;

int main()
{
    f >> n >> s >> t;

    for (int i = 1; i <= n; ++i) {
            int c, p;
        f >> c >> p;
        if (i > t && v.front().pos < i - t)
            v.pop_front();
        while (v.back().cost + (i - v.back().pos) * s > c)
            v.pop_back();
        v.push_back({i, c});

        ans += p*v.front().cost + (i - v.front().pos) * s;

    }
    g << ans;
    return 0;
}