#line 1 "library/Template/template.hpp"
#include <bits/stdc++.h>
using namespace std;

#define rep(i,a,b) for(int i=(int)(a);i<(int)(b);i++)
#define ALL(v) (v).begin(),(v).end()
using ll=long long int;
const int inf = 0x3fffffff;
const ll INF = 0x1fffffffffffffff;
template<typename T>inline bool chmax(T& a,T b){if(a<b){a=b;return 1;}return 0;}
template<typename T>inline bool chmin(T& a,T b){if(a>b){a=b;return 1;}return 0;}
#line 2 "library/Utility/fastio.hpp"
#include <unistd.h>

class FastIO{
    static constexpr int L=1<<16;
    char rdbuf[L];
    int rdLeft=0,rdRight=0;
    inline void reload(){
        int len=rdRight-rdLeft;
        memmove(rdbuf,rdbuf+rdLeft,len);
        rdLeft=0,rdRight=len;
        rdRight+=fread(rdbuf+len,1,L-len,stdin);
    }
    inline bool skip(){
        for(;;){
            while(rdLeft!=rdRight and rdbuf[rdLeft]<=' ')rdLeft++;
            if(rdLeft==rdRight){
                reload();
                if(rdLeft==rdRight)return false;
            }
            else break;
        }
        return true;
    }
    template<typename T,enable_if_t<is_integral<T>::value,int> =0>inline bool _read(T& x){
        if(!skip())return false;
        if(rdLeft+20>=rdRight)reload();
        bool neg=false;
        if(rdbuf[rdLeft]=='-'){
            neg=true;
            rdLeft++;
        }
        x=0;
        while(rdbuf[rdLeft]>='0' and rdLeft<rdRight){
            x=x*10+(neg?-(rdbuf[rdLeft++]^48):(rdbuf[rdLeft++]^48));
        }
        return true;
    }
    template<typename T,enable_if_t<is_floating_point<T>::value,int> =0>inline bool _read(T& x){
        if(!skip())return false;
        if(rdLeft+20>=rdRight)reload();
        bool neg=false;
        if(rdbuf[rdLeft]=='-'){
            neg=true;
            rdLeft++;
        }
        x=0;
        while(rdbuf[rdLeft]>='0' and rdbuf[rdLeft]<='9' and rdLeft<rdRight){
            x=x*10+(rdbuf[rdLeft++]^48);
        }
        if(rdbuf[rdLeft]!='.')return true;
        rdLeft++;
        T base=.1;
        while(rdbuf[rdLeft]>='0' and rdbuf[rdLeft]<='9' and rdLeft<rdRight){
            x+=base*(rdbuf[rdLeft++]^48);
            base*=.1;
        }
        if(neg)x=-x;
        return true;
    }
    inline bool _read(char& x){
        if(!skip())return false;
        if(rdLeft+1>=rdRight)reload();
        x=rdbuf[rdLeft++];
        return true;
    }
    inline bool _read(string& x){
        if(!skip())return false;
        for(;;){
            int pos=rdLeft;
            while(pos<rdRight and rdbuf[pos]>' ')pos++;
            x.append(rdbuf+rdLeft,pos-rdLeft);
            if(rdLeft==pos)break;
            rdLeft=pos;
            if(rdLeft==rdRight)reload();
            else break;
        }
        return true;
    }
    template<typename T>inline bool _read(vector<T>& v){
        for(auto& x:v){
            if(!_read(x))return false;
        }
        return true;
    }

    char wtbuf[L],tmp[50];
    int wtRight=0;
    inline void flush(){
        fwrite(wtbuf,1,wtRight,stdout);
        wtRight=0;
    }
    inline void _write(const char& x){
        if(wtRight>L-32)flush();
        wtbuf[wtRight++]=x;
    }
    inline void _write(const string& x){
        for(auto& c:x)_write(c);
    }
    template<typename T,enable_if_t<is_integral<T>::value,int> =0>inline void _write(T x){
        if(wtRight>L-32)flush();
        if(x==0){
            _write('0');
            return;
        }
        else if(x<0){
            _write('-');
            if (__builtin_expect(x == std::numeric_limits<T>::min(), 0)) {
                switch (sizeof(x)) {
                case 2: _write("32768"); return;
                case 4: _write("2147483648"); return;
                case 8: _write("9223372036854775808"); return;
                }
            }
            x=-x;
        }
        int pos=0;
        while(x!=0){
            tmp[pos++]=char((x%10)|48);
            x/=10;
        }
        rep(i,0,pos)wtbuf[wtRight+i]=tmp[pos-1-i];
        wtRight+=pos;
    }
    template<typename T>inline void _write(const vector<T>& v){
        rep(i,0,v.size()){
            if(i)_write(' ');
            _write(v[i]);
        }
    }
public:
    FastIO(){}
    ~FastIO(){flush();}
    inline void read(){}
    template <typename Head, typename... Tail>inline void read(Head& head,Tail&... tail){
        assert(_read(head));
        read(tail...); 
    }
    template<bool ln=true,bool space=false>inline void write(){if(ln)_write('\n');}
    template <bool ln=true,bool space=false,typename Head, typename... Tail>inline void write(const Head& head,const Tail&... tail){
        if(space)_write(' ');
        _write(head);
        write<ln,true>(tail...); 
    }
};

/**
 * @brief Fast IO
 */
#line 3 "sol.cpp"

template<class T>struct BIT2D{
   struct BIT{
      int n; vector<T> d;
      BIT(){}
      BIT(int _n):d(n=_n){}
      void add(int i,T x){
         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;
      }
   };
   int n; vector<BIT> d;
   vector<int> xs; vector<vector<int>> ys;
   vector<pair<T,T>> p;
   BIT2D(){}
   void push(T x,T y){p.push_back({x,y});}
   void init(){
      rep(i,0,p.size())xs.push_back(p[i].first);
      sort(ALL(xs)); xs.erase(unique(ALL(xs)),xs.end());
      n=xs.size()+1; ys.resize(n);
      rep(j,0,p.size()){
         int s=upper_bound(ALL(xs),p[j].first)-xs.begin();
         for(int i=s;i<n;i+=(i&-i))ys[i].push_back(p[j].second);
      } d.resize(n);
      rep(i,0,n){
         sort(ALL(ys[i])); ys[i].erase(unique(ALL(ys[i])),ys[i].end());
         d[i]=BIT(ys[i].size()+2);
      }
   }
   void add(T x,T y,T z=1){
      int s=upper_bound(ALL(xs),x)-xs.begin();
      for(int i=s;i<n;i+=(i&-i)){
         int idx=upper_bound(ALL(ys[i]),y)-ys[i].begin();
         d[i].add(idx,z);
      }
   }
   T sum(T x,T y){
      T res=0; int s=upper_bound(ALL(xs),x)-xs.begin();
      for(int i=s;i;i-=(i&-i)){
         int idx=upper_bound(ALL(ys[i]),y)-ys[i].begin();
         res+=d[i].sum(idx);
      } return res;
   }
   T sum(T x1,T y1,T x2,T y2){return sum(x2,y2)-sum(x1-1,y2)-sum(x2,y1-1)+sum(x1-1,y1-1);}
};

FastIO io;
int main(){
    int n,k,L,P;
    io.read(n,k,L,P);

    assert(1<=n and n<=34);
    assert(1<=k and k<=n);
    assert(1<=L and L<=1000000000);
    assert(1<=P and P<=1000000000);
    
    vector<int> a(n),b(n);
    rep(i,0,n){
        io.read(a[i],b[i]);
        assert(1<=a[i] and a[i]<=1000000000);
        assert(1<=b[i] and b[i]<=1000000000);
    }

    int n1=n/2,n2=n-n1;
    using Q=pair<int,int>;
    vector zen(n1+1,vector<Q>()),kou(n2+1,vector<Q>());
    BIT2D<int> bit;
    rep(mask,0,1<<n1){
        int l=0,p=0;
        rep(i,0,n1){
            if(mask>>i&1){
                l+=a[i];
                p+=b[i];
            }
            chmin(l,L+1);
            chmin(p,P);
        }
        zen[__builtin_popcountll(mask)].push_back({l,p});
        bit.push(l,p);
    }
    bit.init();
    rep(mask,0,1<<n2){
        int l=0,p=0;
        rep(i,0,n2){
            if(mask>>i&1){
                l+=a[i+n1];
                p+=b[i+n1];
            }
            chmin(l,L+1);
            chmin(p,P);
        }
        kou[__builtin_popcountll(mask)].push_back({l,p});
    }
    ll ret=0;
    rep(x,0,k+1){
        if(x<=n1)for(auto& [l,p]:zen[x])bit.add(l,p);
        if(k-x<=n2)for(auto& [l,p]:kou[k-x])ret+=bit.sum(0,P-p,L-l,P);
    }
    io.write(ret);
    return 0;
}