#include <algorithm>
#include <array>
#include <bitset>
#include <cassert>
#include <chrono>
#include <cmath>
#include <complex>
#include <deque>
#include <forward_list>
#include <fstream>
#include <functional>
#include <iomanip>
#include <ios>
#include <iostream>
#include <limits>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <tuple>
#include <type_traits>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>
using namespace std;
using lint = long long;
using pint = pair<int, int>;
using plint = pair<lint, lint>;
struct fast_ios { fast_ios(){ cin.tie(nullptr), ios::sync_with_stdio(false), cout << fixed << setprecision(20); }; } fast_ios_;
#define ALL(x) (x).begin(), (x).end()
#define FOR(i, begin, end) for(int i=(begin),i##_end_=(end);i<i##_end_;i++)
#define IFOR(i, begin, end) for(int i=(end)-1,i##_begin_=(begin);i>=i##_begin_;i--)
#define REP(i, n) FOR(i,0,n)
#define IREP(i, n) IFOR(i,0,n)
template <typename T, typename V>
void ndarray(vector<T>& vec, const V& val, int len) { vec.assign(len, val); }
template <typename T, typename V, typename... Args> void ndarray(vector<T>& vec, const V& val, int len, Args... args) { vec.resize(len), for_each(begin(vec), end(vec), [&](T& v) { ndarray(v, val, args...); }); }
template <typename T> bool chmax(T &m, const T q) { return m < q ? (m = q, true) : false; }
template <typename T> bool chmin(T &m, const T q) { return m > q ? (m = q, true) : false; }
const std::vector<std::pair<int, int>> grid_dxs{{1, 0}, {-1, 0}, {0, 1}, {0, -1}};
int floor_lg(long long x) { return x <= 0 ? -1 : 63 - __builtin_clzll(x); }
template <class T1, class T2> T1 floor_div(T1 num, T2 den) { return (num > 0 ? num / den : -((-num + den - 1) / den)); }
template <class T1, class T2> std::pair<T1, T2> operator+(const std::pair<T1, T2> &l, const std::pair<T1, T2> &r) { return std::make_pair(l.first + r.first, l.second + r.second); }
template <class T1, class T2> std::pair<T1, T2> operator-(const std::pair<T1, T2> &l, const std::pair<T1, T2> &r) { return std::make_pair(l.first - r.first, l.second - r.second); }
template <class T> std::vector<T> sort_unique(std::vector<T> vec) { sort(vec.begin(), vec.end()), vec.erase(unique(vec.begin(), vec.end()), vec.end()); return vec; }
template <class T> int arglb(const std::vector<T> &v, const T &x) { return std::distance(v.begin(), std::lower_bound(v.begin(), v.end(), x)); }
template <class T> int argub(const std::vector<T> &v, const T &x) { return std::distance(v.begin(), std::upper_bound(v.begin(), v.end(), x)); }
template <class IStream, class T> IStream &operator>>(IStream &is, std::vector<T> &vec) { for (auto &v : vec) is >> v; return is; }

template <class OStream, class T> OStream &operator<<(OStream &os, const std::vector<T> &vec);
template <class OStream, class T, size_t sz> OStream &operator<<(OStream &os, const std::array<T, sz> &arr);
template <class OStream, class T, class TH> OStream &operator<<(OStream &os, const std::unordered_set<T, TH> &vec);
template <class OStream, class T, class U> OStream &operator<<(OStream &os, const pair<T, U> &pa);
template <class OStream, class T> OStream &operator<<(OStream &os, const std::deque<T> &vec);
template <class OStream, class T> OStream &operator<<(OStream &os, const std::set<T> &vec);
template <class OStream, class T> OStream &operator<<(OStream &os, const std::multiset<T> &vec);
template <class OStream, class T> OStream &operator<<(OStream &os, const std::unordered_multiset<T> &vec);
template <class OStream, class T, class U> OStream &operator<<(OStream &os, const std::pair<T, U> &pa);
template <class OStream, class TK, class TV> OStream &operator<<(OStream &os, const std::map<TK, TV> &mp);
template <class OStream, class TK, class TV, class TH> OStream &operator<<(OStream &os, const std::unordered_map<TK, TV, TH> &mp);
template <class OStream, class... T> OStream &operator<<(OStream &os, const std::tuple<T...> &tpl);

template <class OStream, class T> OStream &operator<<(OStream &os, const std::vector<T> &vec) { os << '['; for (auto v : vec) os << v << ','; os << ']'; return os; }
template <class OStream, class T, size_t sz> OStream &operator<<(OStream &os, const std::array<T, sz> &arr) { os << '['; for (auto v : arr) os << v << ','; os << ']'; return os; }
template <class... T> std::istream &operator>>(std::istream &is, std::tuple<T...> &tpl) { std::apply([&is](auto &&... args) { ((is >> args), ...);}, tpl); return is; }
template <class OStream, class... T> OStream &operator<<(OStream &os, const std::tuple<T...> &tpl) { os << '('; std::apply([&os](auto &&... args) { ((os << args << ','), ...);}, tpl); return os << ')'; }
template <class OStream, class T, class TH> OStream &operator<<(OStream &os, const std::unordered_set<T, TH> &vec) { os << '{'; for (auto v : vec) os << v << ','; os << '}'; return os; }
template <class OStream, class T> OStream &operator<<(OStream &os, const std::deque<T> &vec) { os << "deq["; for (auto v : vec) os << v << ','; os << ']'; return os; }
template <class OStream, class T> OStream &operator<<(OStream &os, const std::set<T> &vec) { os << '{'; for (auto v : vec) os << v << ','; os << '}'; return os; }
template <class OStream, class T> OStream &operator<<(OStream &os, const std::multiset<T> &vec) { os << '{'; for (auto v : vec) os << v << ','; os << '}'; return os; }
template <class OStream, class T> OStream &operator<<(OStream &os, const std::unordered_multiset<T> &vec) { os << '{'; for (auto v : vec) os << v << ','; os << '}'; return os; }
template <class OStream, class T, class U> OStream &operator<<(OStream &os, const std::pair<T, U> &pa) { return os << '(' << pa.first << ',' << pa.second << ')'; }
template <class OStream, class TK, class TV> OStream &operator<<(OStream &os, const std::map<TK, TV> &mp) { os << '{'; for (auto v : mp) os << v.first << "=>" << v.second << ','; os << '}'; return os; }
template <class OStream, class TK, class TV, class TH> OStream &operator<<(OStream &os, const std::unordered_map<TK, TV, TH> &mp) { os << '{'; for (auto v : mp) os << v.first << "=>" << v.second << ','; os << '}'; return os; }
#ifdef HITONANODE_LOCAL
const string COLOR_RESET = "\033[0m", BRIGHT_GREEN = "\033[1;32m", BRIGHT_RED = "\033[1;31m", BRIGHT_CYAN = "\033[1;36m", NORMAL_CROSSED = "\033[0;9;37m", RED_BACKGROUND = "\033[1;41m", NORMAL_FAINT = "\033[0;2m";
#define dbg(x) std::cerr << BRIGHT_CYAN << #x << COLOR_RESET << " = " << (x) << NORMAL_FAINT << " (L" << __LINE__ << ") " << __FILE__ << COLOR_RESET << std::endl
#define dbgif(cond, x) ((cond) ? std::cerr << BRIGHT_CYAN << #x << COLOR_RESET << " = " << (x) << NORMAL_FAINT << " (L" << __LINE__ << ") " << __FILE__ << COLOR_RESET << std::endl : std::cerr)
#else
#define dbg(x) ((void)0)
#define dbgif(cond, x) ((void)0)
#endif

template <class S, void (*opadd)(S &, S), void (*opsub)(S &, S), S (*e)(), class Coordinate>
class rangetree_bit {
    int n;
    std::vector<std::pair<Coordinate, Coordinate>> _pts;
    struct BIT {
        std::vector<S> data;
        BIT(int len) : data(len, e()) {}
        void add(int pos, S v) {
            for (pos++; pos and pos <= int(data.size()); pos += pos & -pos)
                opadd(data[pos - 1], v);
        }
        S sum(int r) const {
            S ret = e();
            while (r) opadd(ret, data[r - 1]), r -= r & -r;
            return ret;
        }
    };

    std::vector<std::vector<Coordinate>> _range2ys;
    std::vector<BIT> bits;
    void _add_singlenode(int v, Coordinate y, S val) {
        auto i = std::distance(
            _range2ys[v].begin(), std::lower_bound(_range2ys[v].begin(), _range2ys[v].end(), y));
        bits[v].add(i, val);
    }
    S _get_singlenode(int v, Coordinate y) const {
        auto i = std::distance(
            _range2ys[v].begin(), std::lower_bound(_range2ys[v].begin(), _range2ys[v].end(), y));
        return bits[v].sum(i);
    }
    S _sum(Coordinate xl, Coordinate xr, Coordinate yr) const { // [xl, xr) * (-INF, yr)
        auto compx = [](std::pair<Coordinate, Coordinate> l, std::pair<Coordinate, Coordinate> r) {
            return l.first < r.first;
        };
        int l = n + std::distance(_pts.begin(), std::lower_bound(_pts.begin(), _pts.end(),
                                                                 std::make_pair(xl, yr), compx));
        int r = n + std::distance(_pts.begin(), std::lower_bound(_pts.begin(), _pts.end(),
                                                                 std::make_pair(xr, yr), compx));
        S ret = e();
        while (l < r) {
            if (l & 1) opadd(ret, _get_singlenode(l++, yr));
            if (r & 1) opadd(ret, _get_singlenode(--r, yr));
            l >>= 1, r >>= 1;
        }
        return ret;
    }

public:
    rangetree_bit() = default;
    void add_point(Coordinate x, Coordinate y) noexcept { _pts.emplace_back(x, y); }
    void build() {
        std::sort(_pts.begin(), _pts.end());
        _pts.erase(std::unique(_pts.begin(), _pts.end()), _pts.end());
        n = _pts.size();

        _range2ys.resize(n * 2);
        for (int i = 0; i < n; i++) _range2ys[n + i] = {_pts[i].second};
        for (int i = n - 1; i > 0; i--) {
            auto &lch = _range2ys[i * 2];
            auto &rch = _range2ys[i * 2 + 1];
            std::merge(
                lch.begin(), lch.end(), rch.begin(), rch.end(), std::back_inserter(_range2ys[i]));
            _range2ys[i].erase(
                std::unique(_range2ys[i].begin(), _range2ys[i].end()), _range2ys[i].end());
        }
        for (const auto &v : _range2ys) bits.push_back(BIT(v.size()));
    }
    void add(Coordinate x, Coordinate y, S val) {
        int i = std::distance(
            _pts.begin(), std::lower_bound(_pts.begin(), _pts.end(), std::make_pair(x, y)));
        assert(i < n and _pts[i] == std::make_pair(x, y));
        for (i += n; i; i >>= 1) _add_singlenode(i, y, val);
    }
    S sum(Coordinate xl, Coordinate xr, Coordinate yl, Coordinate yr) const {
        auto ret_r = _sum(xl, xr, yr);
        auto ret_l = _sum(xl, xr, yl);
        opsub(ret_r, ret_l);
        return ret_r;
    }
};

void opadd(int &x, int y) { x += y; }
void opsub(int &x, int y) { x -= y; }
int e() { return 0; }

int main() {
    int N, K, L, P;
    cin >> N >> K >> L >> P;
    vector<lint> A(N), B(N);
    REP(i, N) cin >> A.at(i) >> B.at(i);

    const int nl = N / 2, nr = N - nl;
    dbg(make_tuple(N, nl, nr, K, L, P));

    vector<tuple<int, int, lint>> vs;
    rangetree_bit<int, opadd, opsub, e, lint> tree;

    REP(s, 1 << nl) {
        const int nin = __builtin_popcount(s);
        if (nin > K) continue;
        lint cost = 0, val = 0;
        REP(i, nl) {
            if ((s >> i) & 1) cost += A.at(i), val += B.at(i);
        }
        if (cost > L) continue;
        tree.add_point(cost, val);
        vs.emplace_back(nin, cost, val);
    }
    sort(vs.begin(), vs.end());
    tree.build();
    int ivs = 0;

    vector<tuple<int, int, lint>> rs;
    REP(s, 1 << nr) {
        const int nin = __builtin_popcount(s);
        if (nin > K) continue;
        lint cost = 0, val = 0;
        REP(i, nr) {
            if ((s >> i) & 1) cost += A.at(nl + i), val += B.at(nl + i);
        }
        if (cost > L) continue;
        rs.emplace_back(nin, cost, val);
    }
    sort(rs.rbegin(), rs.rend());

    dbgif(vs.size() <= 100, vs);
    dbgif(rs.size() <= 100, rs);

    lint ret = 0;
    for (auto [sz, rcost, rval] : rs) {
        while (ivs < int(vs.size()) and get<0>(vs.at(ivs)) + sz <= K) {
            auto [lsz, lcost, lval] = vs.at(ivs++);
            tree.add(lcost, lval, 1);
        }
        ret += tree.sum(0, L - rcost + 1, P - rval, 1LL << 60);
        dbgif(rs.size() <= 100, make_tuple(sz, rcost, rval, ret));
    }
    dbg(ivs);
    cout << ret << endl;
}