#line 1 "test.cpp"
//#pragma GCC target("avx2")
//#pragma GCC optimize("O3")
//#pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>
using namespace std;
#ifdef LOCAL
#include <debug.hpp>
#define debug(...) debug_print::multi_print(#__VA_ARGS__, __VA_ARGS__)
#else
#define debug(...) (static_cast<void>(0))
#endif
using ll = long long;
using ld = long double;
using pll = pair<ll,ll>;
using pii = pair<int,int>;
using vi = vector<int>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
using vl = vector<ll>;
using vvl = vector<vl>;
using vvvl = vector<vvl>;
using vpii = vector<pii>;
using vpll = vector<pll>;
using vs = vector<string>;
template<class T> using pq = priority_queue<T,vector<T>,greater<T>>;
#define overload4(_1, _2, _3, _4, name, ...) name
#define overload3(a,b,c,name,...) name
#define rep1(n) for (ll UNUSED_NUMBER = 0; UNUSED_NUMBER < (n); ++UNUSED_NUMBER)
#define rep2(i, n) for (ll i = 0; i < (n); ++i)
#define rep3(i, a, b) for (ll i = (a); i < (b); ++i)
#define rep4(i, a, b, c) for (ll i = (a); i < (b); i += (c))
#define rep(...) overload4(__VA_ARGS__, rep4, rep3, rep2, rep1)(__VA_ARGS__)
#define rrep1(n) for(ll i = (n) - 1;i >= 0;i--)
#define rrep2(i,n) for(ll i = (n) - 1;i >= 0;i--)
#define rrep3(i,a,b) for(ll i = (b) - 1;i >= (a);i--)
#define rrep4(i,a,b,c) for(ll i = (a) + ((b)-(a)-1) / (c) * (c);i >= (a);i -= c)
#define rrep(...) overload4(__VA_ARGS__, rrep4, rrep3, rrep2, rrep1)(__VA_ARGS__)
#define all1(i) begin(i),end(i)
#define all2(i,a) begin(i),begin(i)+a
#define all3(i,a,b) begin(i)+a,begin(i)+b
#define all(...) overload3(__VA_ARGS__, all3, all2, all1)(__VA_ARGS__)
#define sum(...) accumulate(all(__VA_ARGS__),0LL)
template<class T> bool chmin(T &a, const T &b){ if(a > b){ a = b; return 1; } else return 0; }
template<class T> bool chmax(T &a, const T &b){ if(a < b){ a = b; return 1; } else return 0; }
template<class T> auto min(const T& a){ return *min_element(all(a)); }
template<class T> auto max(const T& a){ return *max_element(all(a)); }
template<class... Ts> void in(Ts&... t);
#define INT(...) int __VA_ARGS__; in(__VA_ARGS__)
#define LL(...) ll __VA_ARGS__; in(__VA_ARGS__)
#define STR(...) string __VA_ARGS__; in(__VA_ARGS__)
#define CHR(...) char __VA_ARGS__; in(__VA_ARGS__)
#define DBL(...) double __VA_ARGS__; in(__VA_ARGS__)
#define LD(...) ld __VA_ARGS__; in(__VA_ARGS__)
#define VEC(type, name, size) vector<type> name(size); in(name)
#define VV(type, name, h, w) vector<vector<type>> name(h, vector<type>(w)); in(name)
ll intpow(ll a, ll b){ ll ans = 1; while(b){if(b & 1) ans *= a; a *= a; b /= 2;} return ans;}
ll modpow(ll a, ll b, ll p){ ll ans = 1; a %= p;while(b){ if(b & 1) (ans *= a) %= p; (a *= a) %= p; b /= 2; } return ans; }
ll GCD(ll a,ll b) { if(a == 0 || b == 0) return a + b; if(a % b == 0) return b; else return GCD(b,a%b);}
ll LCM(ll a,ll b) { if(a == 0) return b; if(b == 0) return a;return a / GCD(a,b) * b;}
namespace IO{
#define VOID(a) decltype(void(a))
struct setting{ setting(){cin.tie(nullptr); ios::sync_with_stdio(false);fixed(cout); cout.precision(12);}} setting;
template<int I> struct P : P<I-1>{};
template<> struct P<0>{};
template<class T> void i(T& t){ i(t, P<3>{}); }
void i(vector<bool>::reference t, P<3>){ int a; i(a); t = a; }
template<class T> auto i(T& t, P<2>) -> VOID(cin >> t){ cin >> t; }
template<class T> auto i(T& t, P<1>) -> VOID(begin(t)){ for(auto&& x : t) i(x); }
template<class T, size_t... idx> void ituple(T& t, index_sequence<idx...>){
    in(get<idx>(t)...);}
template<class T> auto i(T& t, P<0>) -> VOID(tuple_size<T>{}){
    ituple(t, make_index_sequence<tuple_size<T>::value>{});}
#undef VOID
}
#define unpack(a) (void)initializer_list<int>{(a, 0)...}
template<class... Ts> void in(Ts&... t){ unpack(IO :: i(t)); }
#undef unpack
//constexpr int mod = 1000000007;
constexpr int mod = 998244353;
static const double PI = 3.1415926535897932;
template <class F> struct REC {
    F f;
    REC(F &&f_) : f(forward<F>(f_)) {}
    template <class... Args> auto operator()(Args &&...args) const { return f(*this, forward<Args>(args)...); }};

#line 3 "library/data-structure/FenwickTree.hpp"
using namespace std;
template <typename T>
struct FenwickTree{
    int N;
    vector<T> data;
    FenwickTree() = default;
    FenwickTree(int size) {init(size);}

    void init(int size) {
        N = size + 2;
        data.assign(N + 1,{});
    }

    T prod(int k) const {
        if (k < 0) return T{};
        T ret{};
        for (++k;k > 0;k -= k & -k) ret += data[k];
        return ret;
    }

    inline T prod(int l,int r) const {return prod(r - 1) - prod(l - 1);}

    inline T get(int k) const {return prod(k) - prod(k - 1); }

    void add(int k, T x) { 
        for(++k;k < N;k += k & -k) data[k] += x;
    }

    int lower_bound(T w) {
        if (w <= 0) return 0;
        int x = 0;
        for(int k = 1 <<__lg(N);k;k >>= 1) {
            if (x + k <= N - 1 && data[x + k] < w) {
                w -= data[x + k];
                x += k;
            }
        }
        return x;
    }
    
    int upper_bound(T w) {
        if (w < 0) return 0;
        int x = 0;
        for(int k = 1 <<__lg(N);k;k >>= 1) {
            if (x + k <= N - 1 && data[x + k] <= w) {
                w -= data[x + k];
                x += k;
            }
        }
        return x;
    }
};
#line 87 "test.cpp"

int main() {
    INT(n,k,L,P);
    vi a(n),b(n);
    rep(i,n) cin >> a[i] >> b[i];
    int n1 = n / 2;
    int n2 = n - n1;
    vector<vpll> v1(n1+1),v2(n2+1);
    rep(i,1<<n1) {
        int c = 0;
        ll w = 0,p = 0;
        rep(j,n1) {
            if(i >> j & 1) {
                c++;
                w += a[j];
                p += b[j];
            }
        }
        v1[c].emplace_back(w,p);
    }
    vl pl;
    rep(i,1<<n2) {
        int c = 0;
        ll w = 0,p = 0;
        rep(j,n2) {
            if(i >> j & 1) {
                c++;
                w += a[j+n1];
                p += b[j+n1];
            }
            pl.emplace_back(p);
        }
        v2[c].emplace_back(w,p);
    }
    sort(all(pl));
    pl.erase(unique(all(pl)),pl.end());
    int si = 0;
    vpll wp;
    ll ans = 0;
    rrep(i,min(k+1,n1+1)) {
        int rm = k - i;
        rep(j,si,min(n2+1,rm+1)) {
            for(auto &x:v2[j]) wp.emplace_back(x);
        }
        si = rm + 1;
        sort(all(wp));
        sort(all(v1[i]),greater<pll>());
        FenwickTree<int> fw((int)pl.size());
        int j = 0;
        for(auto &x:v1[i]) {
            while(j < wp.size() && wp[j].first + x.first <= L) {
                int id = lower_bound(all(pl),wp[j].second) - pl.begin();
                fw.add(id,1);
                j++;
            }
            if(x.second >= P) ans += j;
            else {
                int Q = P - x.second;
                int id2 = lower_bound(all(pl),Q) - pl.begin();
                ans += fw.prod(id2,(int)pl.size());
            }
        }
    }
    cout << ans << '\n';
}