#include <atcoder/all>
#include <iostream> // cout, endl, cin
#include <string> // string, to_string, stoi
#include <vector> // vector
#include <algorithm> // min, max, swap, sort, reverse, lower_bound, upper_bound
#include <utility> // pair, make_pair
#include <tuple> // tuple, make_tuple
#include <cstdint> // int64_t, int*_t
#include <cstdio> // printf
#include <map> // map
#include <queue> // queue, priority_queue
#include <set> // set
#include <stack> // stack
#include <deque> // deque
#include <unordered_map> // unordered_map
#include <unordered_set> // unordered_set
#include <bitset> // bitset
#include <cctype> // isupper, islower, isdigit, toupper, tolower
#include <math.h>
#include <iomanip>
#include <functional>
using namespace std;  
using namespace atcoder;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define repi(i, a, b) for (int i = (int)(a); i < (int)(b); i++)
typedef long long ll;
typedef unsigned long long ull;
const ll inf=1e18;  
using graph = vector<vector<int> > ;
using P= pair<ll,ll>;  
using vi=vector<int>;
using vvi=vector<vi>;
using vll=vector<ll>; 
using vvll=vector<vll>;
using vp=vector<P>;
using vpp=vector<vp>;
using vd=vector<double>;
using vvd =vector<vd>;
//string T="ABCDEFGHIJKLMNOPQRSTUVWXYZ";
//string S="abcdefghijklmnopqrstuvwxyz";
//g++ main.cpp -std=c++17 -I .  
//cout <<setprecision(20);
//cout << fixed << setprecision(10);
//cin.tie(0); ios::sync_with_stdio(false);
const double PI = acos(-1);
int vx[]={0,1,0,-1,-1,1,1,-1},vy[]={1,0,-1,0,1,1,-1,-1};
void putsYes(bool f){cout << (f?"Yes":"No") << endl;}
void putsYES(bool f){cout << (f?"YES":"NO") << endl;}
void putsFirst(bool f){cout << (f?"First":"Second") << endl;}

ll pow_pow(ll x,ll n,ll mod){
    if(n==0) return 1; 
    x%=mod;
    ll res=pow_pow(x*x%mod,n/2,mod);
    if(n&1)res=res*x%mod;
    return res;
}
 struct UnionFind { vector<int> par, siz; UnionFind(int n) : par(n, -1) , siz(n, 1) { } int root(int x) { if (par[x] == -1) return x;
        else return par[x] = root(par[x]);
    }
    bool issame(int x, int y) {
        return root(x) == root(y);
    }
    bool unite(int x, int y) {
        x = root(x), y = root(y);
        if (x == y) return false; 
        if (siz[x] < siz[y]) swap(x, y);
        par[y] = x;
        siz[x] += siz[y];
        return true;
    }
    int size(int x) {
        return siz[root(x)];
    }
};
 
ll gcd(ll x,ll y){
    if(y==0)return x;
    return gcd(y,x%y);
}
 
ll lcm(ll x,ll y){
    return ll(x/gcd(x,y))*y;
}
template<class T> bool chmin(T& a, T b) {
    if (a > b) {
        a = b;
        return true;
    }
    else return false;
}
template<class T> bool chmax(T& a, T b) {
    if (a < b) {
        a = b;
        return true;
    }
    else return false;
}
 
// https://youtu.be/L8grWxBlIZ4?t=9858
// https://youtu.be/ERZuLAxZffQ?t=4807 : optimize
// https://youtu.be/8uowVvQ_-Mo?t=1329 : division
const ll mod =998244353;
struct mint {
  ll x; // typedef long long ll;
  mint(ll x=0):x((x%mod+mod)%mod){}
  mint operator-() const { return mint(-x);}
  mint& operator+=(const mint a) {
    if ((x += a.x) >= mod) x -= mod;
    return *this;
  }
  mint& operator-=(const mint a) {
    if ((x += mod-a.x) >= mod) x -= mod;
    return *this;
  }
  mint& operator*=(const mint a) { (x *= a.x) %= mod; return *this;}
  mint operator+(const mint a) const { return mint(*this) += a;}
  mint operator-(const mint a) const { return mint(*this) -= a;}
  mint operator*(const mint a) const { return mint(*this) *= a;}
  mint pow(ll t) const {
    if (!t) return 1;
    mint a = pow(t>>1);
    a *= a;
    if (t&1) a *= *this;
    return a;
  }
 
  // for prime mod
  mint inv() const { return pow(mod-2);}
  mint& operator/=(const mint a) { return *this *= a.inv();}
  mint operator/(const mint a) const { return mint(*this) /= a;}
};
istream& operator>>(istream& is, const mint& a) { return is >> a.x;}
ostream& operator<<(ostream& os, const mint& a) { return os << a.x;}
// combination mod prime
// https://www.youtube.com/watch?v=8uowVvQ_-Mo&feature=youtu.be&t=1619
struct combination {
  vector<mint> fact, ifact;
  combination(int n):fact(n+1),ifact(n+1) {
    //assert(n < mod);
    fact[0] = 1;
    for (int i = 1; i <= n; ++i) fact[i] = fact[i-1]*i;
    ifact[n] = fact[n].inv();
    for (int i = n; i >= 1; --i) ifact[i-1] = ifact[i]*i;
  }
  mint operator()(int n, int k) {
    if (k < 0 || k > n) return 0;
    return fact[n]*ifact[k]*ifact[n-k];
  } mint p(int n, int k) { return fact[n]*ifact[n-k]; } } c(500000); 
  using vm=vector<mint> ;
using vvm=vector<vm> ;
 
 
ll sqrt_(ll x) {
  ll l = 0, r = ll(3e9)+1;
  while (l+1<r) {
    ll c = (l+r)/2;
    if (c*c <= x) l = c; else r = c;
  }
  return l;
}
 
 
int valid(int x,int y,int h,int w){
  if(x>=0 && y>=0 && x<h && y<w)return 1;
  else return 0;
}
 
struct edge{
  int to; int id;
  edge(int to,int id) : to(to),id(id){}
};
//snuke
template<typename T>
struct Matrix {
  int h, w;
  vector<vector<T> > d;
  Matrix() {}
  Matrix(int h, int w, T val=0): h(h), w(w), d(h, vector<T>(w,val)) {}
  Matrix& unit() {
    //assert(h == w);
    rep(i,h) d[i][i] = 1;
    return *this;
  }
  const vector<T>& operator[](int i) const { return d[i];}
  vector<T>& operator[](int i) { return d[i];}
  Matrix operator*(const Matrix& a) const {
    //assert(w == a.h);
    Matrix r(h, a.w);
    rep(i,h)rep(k,w)rep(j,a.w) {
      r[i][j] += d[i][k]*a[k][j];
    }
    return r;
  }
  Matrix pow(ll t) const {
  //  assert(h == w);
    if (!t) return Matrix(h,h).unit();
    if (t == 1) return *this;
    Matrix r = pow(t>>1);
    r = r*r;
    if (t&1) r = r*(*this);
    return r;
  }
};
using ve=vector<edge>;
using vve=vector<ve>;
//g++ main.cpp -std=c++17 -I .
int cnt=0;
map<ll,ll>d;
void comp(vector<ll>&a){
  set<ll>s(a.begin(),a.end());
  for(auto y:s)d[y]=cnt++;
  for(auto&y:a)y=d[y];
}   
struct S{
  int num;ll cost;ll value;
  S(int num=0,ll cost=0,ll value=0) : num(num),cost(cost),value(value) {}
};
int main(){cin.tie(0);ios::sync_with_stdio(false);
   int n,k,l,p; cin >> n >> k >> l >> p;
   vp v(n);rep(i,n)cin >> v[i].first >> v[i].second;
   vp odds,evens;
   rep(i,n){
     if(i%2==0)odds.push_back(v[i]);
     else evens.push_back(v[i]);
   } 
   int si=odds.size(),si2=evens.size();
   vector<S> a,b;
   rep(bit,1<<si){
     S now;
     rep(i,si){
       if(bit>>i&1){
         now.num++;
         now.cost+=odds[i].first;
         now.value+=odds[i].second;
       }
     }
     a.push_back(now);
   }
   rep(bit,1<<si2){
     S now;
     rep(i,si2){
       if(bit>>i&1){
         now.num++;
         now.cost+=evens[i].first;
         now.value+=evens[i].second;
       }
     }
     b.push_back(now);
   }
   vll vs;vs.push_back(l);vs.push_back(p);
   rep(i,a.size())a[i].cost=l-a[i].cost,a[i].value=p-a[i].value;
   for(auto u:a)vs.push_back(u.cost),vs.push_back(u.value);
   for(auto u:b)vs.push_back(u.cost),vs.push_back(u.value);
   comp(vs);
   int N=cnt;
   rep(i,a.size())a[i].cost=d[a[i].cost],a[i].value=d[a[i].value];
   rep(i,b.size())b[i].cost=d[b[i].cost],b[i].value=d[b[i].value];
   auto F=[&](S a,S b){return a.num>b.num;};
   auto F2=[&](S a,S b){return a.num<b.num;};
   sort(a.begin(),a.end(),F);
   sort(b.begin(),b.end(),F2);
   int last=-1;
   int last2=-1;
   priority_queue<P,vector<P>,greater<P> > q,q2;
   ll ans=0;
   auto f=[&](){
       fenwick_tree<ll> fw(N);
       while(q2.size() || q.size()){
         if(q2.size() && q.size()){
           if(q2.top().first<=q.top().first){
             fw.add(q2.top().second,1);
             q2.pop();
           }
           else {
             ans+=fw.sum(q.top().second,N);
             q.pop();
           }
         }
         else if(q2.size())break;
         else {
             ans+=fw.sum(q.top().second,N);
             q.pop();
         }
       } 
   };
   for(int i=si; i>=0; i--){
     while(q.size())q.pop();
     int nowlast=last,nowlast2=last2;
     last++;
     for(int j=0; j<a.size(); j++){
       if(a[j].num==i){q.push(P(a[j].cost,a[j].value));nowlast++;}
     }
     last2++;
     while(q2.size())q2.pop();
     for(int j=0; j<b.size(); j++){
       if(b[j].num+i<=k){q2.push(P(b[j].cost,b[j].value));nowlast2++;}
       else break;
     }
     last=nowlast;last2=nowlast2;
     f();
   }
   cout << ans << endl;
}