#ifdef t9unkubj
#include"template.h"
//#include"template_no_debug.h"
#else
#undef _GLIBCXX_DEBUG
#pragma GCC optimize("O3")
#define dbg(...) 199958
using namespace std;
#include<bits/stdc++.h>
using uint=unsigned;
using ll=long long;
using ull=unsigned long long;
using ld=long double;
using pii=pair<int,int>;
using pll=pair<ll,ll>;
template<class T>using vc=vector<T>;
template<class T>using vvc=vc<vc<T>>;
template<class T>using vvvc=vvc<vc<T>>;
using vi=vc<int>;
using vvi=vc<vi>;
using vvvi=vc<vvi>;
using vl=vc<ll>;
using vvl=vc<vl>;
using vvvl=vc<vvl>;
template<class T>using smpq=priority_queue<T,vector<T>,greater<T>>;
template<class T>using bipq=priority_queue<T>;
#define rep(i,n) for(ll i=0;i<(ll)(n);i++)
#define REP(i,j,n) for(ll i=(j);i<(ll)(n);i++)
#define DREP(i,n,m) for(ll i=(n);i>=(m);i--)
#define drep(i,n) for(ll i=((n)-1);i>=0;i--)
#define all(x) x.begin(),x.end()
#define rall(x) x.rbegin(),x.rend()
#define mp make_pair
#define pb push_back
#define eb emplace_back
#define fi first
#define se second
#define is insert
#define bg begin()
#define ed end()
void scan(int&a) { cin >> a; }
void scan(ll&a) { cin >> a; }
void scan(string&a) { cin >> a; }
void scan(char&a) { cin >> a; }
void scan(uint&a) { cin >> a; }
void scan(ull&a) { cin >> a; }
void scan(bool&a) { cin >> a; }
void scan(ld&a){ cin>> a;}
template<class T> void scan(vector<T>&a) { for(auto&x:a) scan(x); }
void read() {}
template<class Head, class... Tail> void read(Head&head, Tail&... tail) { scan(head); read(tail...); }
#define INT(...) int __VA_ARGS__; read(__VA_ARGS__);
#define LL(...) ll __VA_ARGS__; read(__VA_ARGS__);
#define ULL(...) ull __VA_ARGS__; read(__VA_ARGS__);
#define STR(...) string __VA_ARGS__; read(__VA_ARGS__);
#define CHR(...) char __VA_ARGS__; read(__VA_ARGS__);
#define DBL(...) double __VA_ARGS__; read(__VA_ARGS__);
#define LD(...) ld __VA_ARGS__; read(__VA_ARGS__);
#define VC(type, name, ...) vector<type> name(__VA_ARGS__); read(name);
#define VVC(type, name, size, ...) vector<vector<type>> name(size, vector<type>(__VA_ARGS__)); read(name);
void print(int a) { cout << a; }
void print(ll a) { cout << a; }
void print(string a) { cout << a; }
void print(char a) { cout << a; }
void print(uint a) { cout << a; }
void print(bool a) { cout << a; }
void print(ull a) { cout << a; }
void print(double a) { cout << a; }
void print(ld a){ cout<< a; }
template<class T> void print(vector<T>a) { for(int i=0;i<(int)a.size();i++){if(i)cout<<" ";print(a[i]);}cout<<endl;}
void PRT() { cout <<endl; return ; }
template<class T> void PRT(T a) { print(a); cout <<endl; return; }
template<class Head, class... Tail> void PRT(Head head, Tail ... tail) { print(head); cout << " "; PRT(tail...); return; }
template<class T,class F>
bool chmin(T &x, F y){
    if(x>y){
        x=y;
        return true;
    }
    return false;
}
template<class T, class F>
bool chmax(T &x, F y){
    if(x<y){
        x=y;
        return true;
    }
    return false;
}
void YesNo(bool b){
    cout<<(b?"Yes":"No")<<endl;
}
void Yes(){
    cout<<"Yes"<<endl;
}
void No(){
    cout<<"No"<<endl;
}
template<class T>
int popcount(T n){
    return __builtin_popcountll(n);
}
template<class T>
T sum(vc<T>&a){
    return accumulate(all(a),T(0));
}
template<class T>
T max(vc<T>&a){
    return *max_element(all(a));
}
template<class T>
T min(vc<T>&a){
    return *min_element(all(a));
}
template<class T>
void unique(vc<T>&a){
    a.erase(unique(all(a)),a.end());
}
vvi readgraph(int n,int m,int off = -1){
    vvi g(n);
    rep(i, m){
        int u,v;
        cin>>u>>v;
        u+=off,v+=off;
        g[u].push_back(v);
        g[v].push_back(u);
    }
    return g;
}
vvi readtree(int n,int off=-1){
    return readgraph(n,n-1,off);
}
template<class T>
vc<T> presum(vc<T> &a){
    vc<T> ret(a.size()+1);
    rep(i,a.size())ret[i+1]=ret[i]+a[i];
    return ret;
}
template<class T, class F>
vc<T> &operator+=(vc<T> &a,F b){
    for (auto&v:a)v += b;
    return a;
}
template<class T, class F>
vc<T> &operator-=(vc<T>&a,F b){
    for (auto&v:a)v-=b;
    return a;
}
template<class T, class F>
vc<T> &operator*=(vc<T>&a,F b){
    for (auto&v:a)v*=b;
    return a;
}
#endif
double pass_time=0;
#include<vector>
template <class T = long long >
struct BIT {
    int n;
    std::vector<T>data;
    void add(int i,T x){
        assert(i>=0&&i<n);
        i++;
        for(;i<=n;){
            data[i - 1] += x;
            i += (i & -i);
        }
        return;
    }   
    T internal_sum(int r){
        T ret = 0;
        for(;r;){
            ret += data[r - 1];
            r -= (r & -r);
        }
        return ret;
    }
    T sum(int l,int r){
        return internal_sum(r)-internal_sum(l);
    }
    BIT():n(0), data(0) {}
    BIT(int N):n(N), data(N) {}
    BIT(std::vector<T>& a){
        n = a.size();
        data.assign(n, 0);
        for (int i = 0; i < n; i++)add(i, a[i]);
    }
    int lower_bound(T w) { 
    if (w <= 0) {
        return 0;
    } else {
        int x = 0, r = 1;
        while (r < n) r = r << 1;
        for (int len = r; len > 0; len = len >> 1) { 
            if (x + len < n && data[x + len] < w) {
                w -= data[x + len];
                x += len;
            }
        }
        return x;
    }
}
};
void solve(){
    INT(n,k,l,p);
    vi a(n),b(n);
    rep(i,n)cin>>a[i]>>b[i];
    int half=n/2;
    vc<array<ll,3>>cs;
    rep(i,1<<half){
        ll cost=0,val=0;
        rep(j,half)if(i>>j&1)cost+=a[j],val+=b[j];
        cs.pb({cost,val,popcount(i)});
    }
    int half2=n-half;
    vc<array<ll,3>>cs2;
    rep(i,1<<half2){
        ll cost=0,val=0;
        rep(j,half2)if(i>>j&1)cost+=a[j+half],val+=b[j+half];
        cs2.pb({l-cost,p-val,popcount(i)});
    }

    map<ll,ll>ma;
    for(auto&[x,y,i]:cs)ma[y]=0;
    for(auto&[x,y,i]:cs2)ma[y]=0;
    int id=0;
    for(auto&[x,y]:ma)y=id++;
    int K=ma.size();
    vc<BIT<int>>bit(n+1,BIT<int>(K));
    vc<array<ll,4>>ev;
    for(auto&[x,y,i]:cs)ev.pb({x,0,y,i});
    for(auto&[x,y,i]:cs2)ev.pb({x,1,y,k-i});
    sort(all(ev));
    ll ans=0;
    for(auto [x,t,y,i]:ev){
        if(t==0)bit[i].add(ma[y],1);
        else rep(j,i+1)ans+=bit[j].sum(ma[y],K);
    }
    PRT(ans);
}  

signed main(){
    cin.tie(0)->sync_with_stdio(0);
    pass_time=clock();
    int t=1;
    //cin>>t;
    while(t--)solve();
    pass_time=clock()-pass_time;
    dbg(pass_time/CLOCKS_PER_SEC);
}