#include<bits/stdc++.h>
using namespace std;
using lint =long long;
#define rep(i,n) for(lint i=0;i<n;++i)
#define all(n) (n).begin(),(n).end()
#include<ext/pb_ds/assoc_container.hpp>
#include<ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/priority_queue.hpp>
#include<ext/pb_ds/tag_and_trait.hpp>
template<typename T>using pbds=__gnu_pbds::tree<T,__gnu_pbds::null_type,less<T>,__gnu_pbds::rb_tree_tag,__gnu_pbds::tree_order_statistics_node_update>;
template<typename T>using pbds_map=__gnu_pbds::tree<T,T,less<T>,__gnu_pbds::rb_tree_tag,__gnu_pbds::tree_order_statistics_node_update>;
template<typename T,typename E>using hash_map=__gnu_pbds::gp_hash_table<T,E>;
template<typename T>using pqueue =__gnu_pbds::priority_queue<T, greater<T>,__gnu_pbds::rc_binomial_heap_tag>;

int main(){
    lint n,k,l,p;
    cin>>n>>k>>l>>p;
    vector<lint> a(n),b(n);
    rep(i,n)cin>>a[i]>>b[i];
    vector<vector<pair<lint,lint>>>s;
    vector<vector<pair<lint,lint>>>t;
    s.resize(n);
    t.resize(n);
    rep(i,1<<(n/2)){
        lint c=0,v=0;
        rep(j,n/2){
            if(i>>j&1){
                c+=a[j];
                v+=b[j];
            }
        }
        s[__builtin_popcountll(i)].emplace_back(c,v);
    }
        rep(i,1<<(n-n/2)){
        lint c=0,v=0;
        rep(j,n-n/2){
            if(i>>j&1){
                c+=a[j+n/2];
                v+=b[j+n/2];
            }
        }
        t[__builtin_popcountll(i)].emplace_back(c,v);
    }
    rep(i,n)sort(all(s[i]));
    rep(i,n)sort(all(t[i]));
    rep(i,n)reverse(all(t[i]));
    lint ans=0;
    rep(i,k+1){
        rep(j,k-i+1){
            lint now=0;
            pbds<pair<lint,lint>>r;
            for(auto [c,v]:t[j]){
                // cerr<<c<<" "<<v<<endl;
                while(now<(int)s[i].size()&&s[i][now].first+c<=l){
                    r.insert(make_pair(s[i][now].second,now));
                    now++;
                }
                ans+=(int)r.size()-r.order_of_key(make_pair(p-v,-1LL));
            }
        }
    }
    cout<<ans<<endl;
}