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

ifstream fin("lupu.in");
ofstream fout("lupu.out");

priority_queue<pair<int, int>> PQ;

int main() {
    int n, x, l;
    fin >> n >> x >> l;
    int maxim = 0;
    for (int i = 1; i <= n; ++i) {
        int d, a;
        fin >> d >> a;

        int ind = (x - d) / l + 1;
        PQ.push({ind, a});
        maxim = max(maxim, ind);
    }

    int cnt = 0;
    int sum = 0;
    while (PQ.size() && cnt < maxim) {
        sum += PQ.top().second;
        PQ.pop();
        cnt++;
    }

    fout << sum;
    return 0;
}