#include <fstream>
#include <set>
using namespace std;

long long n, x, l, pas;
long long c1, c2, sol = 0;
set < pair <long long, long long> > S;
int main()
{
    ifstream f("lupu.in");
    ofstream g("lupu.out");

    f >> n >> x >> l;
    for (int i = 1; i <= n; ++i)
    {
        f >> c1 >> c2;
        S.insert(make_pair(-c2, c1));
    }

    for (; S.size() > 0; )
    {
        while ((S.begin() -> second) + pas > x)
        {
            S.erase(*S.begin());
            if (S.size() == 0) break ;
        }

        if (S.size() == 0) break ;

        sol += -(S.begin() -> first);
        S.erase(*S.begin());
        pas += l;
    }

    g << sol << '\n';
    g.close();
    return 0;
}