#include <iostream>
#include <fstream>

using namespace std;

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

struct doua
{

    long long c;
    long long p;
};

int n,s,t,dq[100005];
doua a[100005];

int main()
{
    int i;
    long long int suma = 0;
    int st = 0;
    int dr = -1;
    in >> n >> s >> t;
    t++;
    for (i=1; i<=n; i++)
    {
        in >> a[i].c >> a[i].p;
    }
    for (i=1; i<=n; i++)
    {
        if (st <= dr && dq[st] == i - t)
        {
            st++;
        }

        while (st <= dr && a[i].c <= a[dq[dr]].c + s*(i - dq[dr]))
        {
            dr--;
        }

        dq[++dr] = i;
        suma += (a[dq[st]].c + s * (i-dq[st])) * a[i].p;

    }
    out << suma;
    return 0;
}