#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
#define FOR(i,m,n) for(int i=(m);i<(n);++i)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()
using ll = long long;
constexpr int INF = 0x3f3f3f3f;
constexpr long long LINF = 0x3f3f3f3f3f3f3f3fLL;
constexpr double EPS = 1e-8;
constexpr int MOD = 998244353;
// constexpr int MOD = 1000000007;
constexpr int DY4[]{1, 0, -1, 0}, DX4[]{0, -1, 0, 1};
constexpr int DY8[]{1, 1, 0, -1, -1, -1, 0, 1};
constexpr int DX8[]{0, -1, -1, -1, 0, 1, 1, 1};
template <typename T, typename U>
inline bool chmax(T& a, U b) { return a < b ? (a = b, true) : false; }
template <typename T, typename U>
inline bool chmin(T& a, U b) { return a > b ? (a = b, true) : false; }
struct IOSetup {
  IOSetup() {
    std::cin.tie(nullptr);
    std::ios_base::sync_with_stdio(false);
    std::cout << fixed << setprecision(20);
  }
} iosetup;

template <typename Abelian>
struct FenwickTree {
  explicit FenwickTree(const int n, const Abelian ID = 0)
      : n(n), ID(ID), data(n, ID) {}

  void add(int idx, const Abelian val) {
    for (; idx < n; idx |= idx + 1) {
      data[idx] += val;
    }
  }

  Abelian sum(int idx) const {
    Abelian res = ID;
    for (--idx; idx >= 0; idx = (idx & (idx + 1)) - 1) {
      res += data[idx];
    }
    return res;
  }

  Abelian sum(const int left, const int right) const {
    return left < right ? sum(right) - sum(left) : ID;
  }

  Abelian operator[](const int idx) const { return sum(idx, idx + 1); }

  int lower_bound(Abelian val) const {
    if (val <= ID) return 0;
    int res = 0, exponent = 1;
    while (exponent <= n) exponent <<= 1;
    for (int mask = exponent >> 1; mask > 0; mask >>= 1) {
      const int idx = res + mask - 1;
      if (idx < n && data[idx] < val) {
        val -= data[idx];
        res += mask;
      }
    }
    return res;
  }

 private:
  const int n;
  const Abelian ID;
  std::vector<Abelian> data;
};

vector<vector<pair<ll, ll>>> enu(const vector<int>& a, const vector<int>& b) {
  const int n = a.size();
  vector<vector<pair<ll, ll>>> res(n + 1);
  REP(bit, 1 << n) {
    ll cost = 0, value = 0;
    REP(i, n) {
      if (bit >> i & 1) {
        cost += a[i];
        value += b[i];
      }
    }
    res[__builtin_popcount(bit)].emplace_back(cost, value);
  }
  return res;
}

int main() {
  int n, k, l, p; cin >> n >> k >> l >> p;
  vector<int> a(n), b(n); REP(i, n) cin >> a[i] >> b[i];
  auto le = enu(vector(a.begin(), next(a.begin(), n / 2)), vector(b.begin(), next(b.begin(), n / 2)));
  auto ri = enu(vector(next(a.begin(), n / 2), a.end()), vector(next(b.begin(), n / 2), b.end()));
  vector<ll> values;
  values.reserve(1 << ((n + 1) / 2));
  for (const vector<pair<ll, ll>>& ri_i : ri) {
    for (const auto& [_, v] : ri_i) values.emplace_back(v);
  }
  sort(ALL(values));
  values.erase(unique(ALL(values)), values.end());
  const int m = values.size();
  int ri_index = 0;
  vector<pair<ll, ll>> prs;
  ll ans = 0;
  for (int i = min(static_cast<int>(le.size()) - 1, k); i >= 0; --i) {
    for (; ri_index < ri.size() && ri_index + i <= k; ++ri_index) {
      const int s = prs.size();
      sort(ALL(ri[ri_index]));
      prs.resize(s + ri[ri_index].size());
      copy(ALL(ri[ri_index]), next(prs.begin(), s));
      inplace_merge(prs.begin(), next(prs.begin(), s), prs.end());
    }
    FenwickTree<int> bit(m);
    int j = 0;
    sort(ALL(le[i]), greater<pair<ll, ll>>());
    for (const auto [c_le, v_le] : le[i]) {
      for (; j < prs.size() && prs[j].first + c_le <= l; ++j) {
        bit.add(lower_bound(ALL(values), prs[j].second) - values.begin(), 1);
      }
      ans += bit.sum(lower_bound(ALL(values), p - v_le) - values.begin(), m);
      // cout << '{' << c_le << ',' << v_le << "} " << ans << '\n';
    }
    // cout << i << ' ' << ri_index - 1 << ": " << ans << '\n';
  }
  cout << ans << '\n';
  // int answer = 0;
  // const vector<vector<pair<ll, ll>>> enu_all = enu(a, b);
  // REP(i, k + 1) {
  //   for (const auto& [c, v] : enu_all[i]) {
  //     answer += c <= l && v >= p;
  //   }
  // }
  // assert(answer == ans);
  return 0;
}