#include <bits/stdc++.h>
using namespace std;

template <typename T>
struct BinaryIndexedTree {
    int N;
    vector<T>bit;
    BinaryIndexedTree(){}
    BinaryIndexedTree(int x) {
        N = x;
        bit.resize(x+1);
    }
    void add(int x,T y) {
        while(x <= N) {
            bit[x] += y;
            x += x&-x;
        }
    }
    T sum(int x) {
        T res = 0;
        while(x) {
            res += bit[x];
            x -= x&-x;
        }
        return res;
    }
    inline T sum(int l, int r) {//[l,r]
        return sum(r)-sum(l-1);
    }
    inline T operator[](int k) {
        return sum(k)-sum(k-1);
    }
};

int main() {
    int N,K,L,P;
    cin >> N >> K >> L >> P;
    vector<int>A(N),B(N);
    for(int i = 0; i < N; i++) {
        cin >> A[i] >> B[i];
    }
    int a = N/2,b = N-a;
    vector<vector<pair<int,int>>>tmp1(a+1),tmp2(b+1);
    for(int i = 0; i < (1 << a); i++) {
        long long sum1 = 0,sum2 = 0;
        for(int j = 0; j < a; j++) {
            if(1 & (i >> j)) {
                sum1 += A[j];
                sum2 += B[j];
            }
        }
        if(sum1 <= L) {
            if(sum2 >= P) sum2 = P;
            tmp1[__builtin_popcount(i)].push_back({sum1,sum2});
        }
    }
    for(int i = 0; i < (1 << b); i++) {
        long long sum1 = 0,sum2 = 0;
        for(int j = 0; j < b; j++) {
            if(1 & (i >> j)) {
                sum1 += A[a+j];
                sum2 += B[a+j];
            }
        }
        if(sum1 <= L) {
            if(sum2 >= P) sum2 = P;
            tmp2[__builtin_popcount(i)].push_back({sum1,sum2});
        }
    }
    long long ans = 0;
    for(int i = min(a,K); i >= 0; i--) {
        vector<pair<int,int>>c,d;
        for(int j = 0; j < tmp1[i].size(); j++) {
            c.push_back(tmp1[i][j]);
        }
        sort(c.rbegin(),c.rend());
        vector<int>cmp;
        for(int j = min(b,K-i); j >= 0; j--) {
            for(int k = 0; k < tmp2[j].size(); k++) {
                d.push_back(tmp2[j][k]);
                cmp.push_back(tmp2[j][k].second);
            }
        }
        sort(d.begin(),d.end());
        sort(cmp.begin(),cmp.end());
        cmp.erase(unique(cmp.begin(),cmp.end()),cmp.end());
        BinaryIndexedTree<int>bit(cmp.size());
        int now = 0;
        for(int j = 0; j < c.size(); j++) {
            while(now < d.size() && c[j].first+d[now].first <= L) {
                int it = lower_bound(cmp.begin(),cmp.end(),d[now].second)-cmp.begin();
                bit.add(it+1,1);
                now++;
            }
            int it = lower_bound(cmp.begin(),cmp.end(),P-c[j].second)-cmp.begin();
            if(it < cmp.size()) {
                ans += bit.sum(it+1,cmp.size());
            }
        }
    }
    cout << ans << endl;
}