#include <bits/stdc++.h>
using namespace std;
int n, p1, p2, tot1, tot2;
long long L, W, ans, a[100005], b[100005];
int main() {
  scanf("%d%lld%lld", &n, &L, &W);
  long long t;
  int v;
  for (int i = 1; i <= n; ++i) {
    scanf("%lld%d", &t, &v);
    if (v == 1)
      a[++tot1] = t;
    else
      b[++tot2] = t;
  }
  sort(a + 1, a + tot1 + 1), sort(b + 1, b + tot2 + 1);
  for (p1 = p2 = 1; p1 <= tot1; ++p1) {
    while (p2 <= tot2 && (b[p2] - a[p1] + L) * W <= abs(b[p2] + a[p1] + L) &&
           (p2++, 1))
      ;
    ans += tot2 - p2 + 1;
  }
  printf("%lld\n", ans);
  return 0;
}
