#include <fstream>

using namespace std;

ifstream f("branza.in");
ofstream g("branza.out");
int c[100001], p, d[100001];
int main()
{
    int n, s, t, i, st = 0, dr = -1;
    long long sum = 0;
    f >> n >> s >> t;
    for (i = 0; i < n; i++)
    {
        f >> c[i] >> p;
        if (st <= dr && d[st] == i - t)
            st++;
        while (st <= dr && c[i] <= c[d[dr]] + s * (i-d[dr]))
            dr--;
        d[++dr] = i;
        sum += p * (c[d[st]] + s * (i - d[st]));
    }
    g << sum;
    return 0;
}