#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (n); ++i)
#define rep1(i,n) for(int i = 1; i <= (n); ++i)
#define drep(i,n) for(int i = (n)-1; i >= 0; --i)
#define srep(i,s,t) for (int i = s; i < (t); ++i)
#define rng(a) a.begin(),a.end()
#define rrng(a) a.rbegin(),a.rend()
#define fi first
#define se second
#define pb push_back
#define eb emplace_back
#define pob pop_back
#define sz(x) (int)(x).size()
#define pcnt __builtin_popcountll
#define snuke srand((unsigned)clock()+(unsigned)time(NULL));
#define newline puts("")
using namespace std;
template<typename T> using vc = vector<T>;
template<typename T> using vv = vc<vc<T>>;
template<typename T> using PQ = priority_queue<T,vc<T>,greater<T>>;
using uint = unsigned; using ull = unsigned long long;
using vi = vc<int>; using vvi = vv<int>; using vvvi = vv<vi>;
using ll = long long; using vl = vc<ll>; using vvl = vv<ll>; using vvvl = vv<vl>;
using P = pair<ll,ll>; using vp = vc<P>; using vvp = vv<P>;
int geti(){int x;scanf("%d",&x);return x;}
vi pm(int n, int s=0) { vi a(n); iota(rng(a),s); return a;}
template<typename T>istream& operator>>(istream&i,vc<T>&v){rep(j,sz(v))i>>v[j];return i;}
template<typename T>string join(const T&v,const string& d=""){stringstream s;rep(i,sz(v))(i?s<<d:s)<<v[i];return s.str();}
template<typename T>ostream& operator<<(ostream&o,const vc<T>&v){if(sz(v))o<<join(v," ");return o;}
template<typename T1,typename T2>istream& operator>>(istream&i,pair<T1,T2>&v){return i>>v.fi>>v.se;}
template<typename T1,typename T2>ostream& operator<<(ostream&o,const pair<T1,T2>&v){return o<<v.fi<<","<<v.se;}
template<typename T1,typename T2>void operator--(pair<T1,T2>&a,int){a.fi--;a.se--;}
template<typename T>void operator--(vc<T>&a,int){for(T&x:a)x--;}
template<typename T>void operator++(vc<T>&a,int){for(T&x:a)x++;}
template<typename T>void operator+=(vc<T>&a,T b){for(T&x:a)x+=b;}
template<typename T>void operator+=(vc<T>&a,const vc<T>&b){a.insert(a.end(),rng(b));}
template<typename T1,typename T2>bool mins(T1& x,const T2&y){if(x>y){x=y;return true;}else return false;}
template<typename T1,typename T2>bool maxs(T1& x,const T2&y){if(x<y){x=y;return true;}else return false;}
template<typename Tx, typename Ty>Tx dup(Tx x, Ty y){return (x+y-1)/y;}
template<typename T>ll suma(const vc<T>&a){ll res(0);for(auto&&x:a)res+=x;return res;}
template<typename T>ll suma(const vv<T>&a){ll res(0);for(auto&&x:a)res+=suma(x);return res;}
template<typename T>void uni(T& a){sort(rng(a));a.erase(unique(rng(a)),a.end());}
template<typename T>void prepend(vc<T>&a,const T&x){a.insert(a.begin(),x);}
const double eps = 1e-10;
const ll LINF = 1001002003004005006ll;
const int INF = 1001001001;
#define dame { puts("-1"); return;}
#define yes { puts("Yes"); return;}
#define no { puts("No"); return;}
#define ret(x) { cout<<(x)<<endl; return;}
#define yn {puts("Yes");}else{puts("No");}
const int MX = 200005;

// coordinate compression
template<typename T=int>
struct X {
  bool ini; vc<T> d;
  X(): ini(false) {}
  /*
  X(vc<T>& a): ini(true), d(a) {
    init();
    for (T& na : a) na = (*this)(na);
  }// int only */
  void add(const T& x) { assert(!ini); d.pb(x);}
  void init() {
    sort(rng(d));
    d.erase(unique(rng(d)), d.end());
    ini = true;
  }
  int size() { if (!ini) init(); return sz(d);}
  T operator[](int i) { if (!ini) init(); return d[i];}
  int operator()(const T& x) {
    if (!ini) init();
    return upper_bound(rng(d),x)-d.begin()-1;
  }
  bool in(const T& x) { if (!ini) init(); return binary_search(rng(d),x);}
};
//

// Binary Indexed Tree
template<typename T=int>
struct bit {
  int n; vector<T> d;
  bit() {}
  bit(int mx): n(mx+1), d(mx+1) {}
  void add(int i, T x=1) {
    for (++i;i<n;i+=i&-i) d[i] += x;
  }
  T sum(int i) {
    T x = 0;
    for (++i;i;i-=i&-i) x += d[i];
    return x;
  }
  T sum(int l, int r) { return sum(r-1)-sum(l-1);}
};
//

struct Solver {
  void solve() {
    int n,k,l,p;
    scanf("%d%d%d%d",&n,&k,&l,&p);
    vp s, t;
    rep(i,n) {
      int a,b;
      scanf("%d%d",&a,&b);
      s.eb(a,b);
      swap(s,t);
    }
    auto f = [&](vp s) {
      vvp res(1,vp(1));
      for (auto [a,b] : s) {
        res.pb(vp());
        drep(i,sz(res)-1) {
          for (auto [na,nb] : res[i]) res[i+1].eb(na+a,nb+b);
        }
      }
      return res;
    };
    vvp ps = f(s), pt = f(t);
    rep(i,sz(ps)) sort(rng(ps[i]));
    rep(i,sz(pt)) sort(rrng(pt[i]));
    ll ans = 0;
    rep(si,sz(ps))rep(ti,sz(pt)) if (si+ti<=k) {
      vp& s = ps[si];
      vp& t = pt[ti];
      X<ll> xs;
      rep(i,sz(s)) xs.add(-s[i].se);
      bit<ll> d(sz(xs));
      int i = 0;
      for (auto [a,b] : t) {
        while (i < sz(s) && s[i].fi <= l-a) {
          d.add(xs(-s[i].se)); i++;
        }
        ans += d.sum(xs(-(p-b)));
      }
    }
    cout<<ans<<endl;
  }
};

int main() {
  // cin.tie(nullptr); ios::sync_with_stdio(false);
  int ts = 1;
  // scanf("%d",&ts);
  rep1(ti,ts) {
    Solver solver;
    solver.solve();
  }
  return 0;
}