#include <bits/stdc++.h>
using namespace std;
ifstream f("branza.in");
ofstream g("branza.out");
long long n, s, t, c, p;
long long ans = 0;
deque <long long> d, poz;

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

    for (int i=1; i<=n; ++i) {
        f >> c >> p;

        while (!d.empty() && c < (d.back() + (i-poz.back())*s) ) {
            d.pop_back();   poz.pop_back();
        }

        d.push_back (c);   poz.push_back (i);

        while (poz.front() < i-t) {
            d.pop_front();  poz.pop_front();
        }

        ans += (d.front() + (i-poz.front())*s) * p;
    }

    g << ans;
    return 0;
}