#include <algorithm>
#include <iostream>
#include <numeric>
#include <vector>

#include <atcoder/fenwicktree>

std::vector<std::vector<std::pair<int64_t, int64_t>>> enumerate_all(
    const size_t N,
    const size_t K,
    const std::vector<int64_t> w,
    const std::vector<int64_t> v
) {
    std::vector<std::vector<std::pair<int64_t, int64_t>>> res(K + 1);
    res[0].emplace_back(0, 0);
    for (size_t i = 0; i < N; ++i) {
        std::vector<std::size_t> mid(K + 1);
        for (size_t j = 1; j <= K; ++j) {
            mid[j] = res[j].size();
        }
        for (size_t j = K; j --> 0;) {
            for (const auto& [wsum, vsum] : res[j]) {
                res[j + 1].emplace_back(wsum + w[i], vsum + v[i]);
            }
        }
        for (size_t j = 1; j <= K; ++j) {
            std::inplace_merge(res[j].begin(), res[j].begin() + mid[j], res[j].end());
        }
    }
    return res;
}

int64_t solve(
    const size_t N,
    const size_t K,
    const int64_t W,
    const int64_t V,
    const std::vector<int64_t> w,
    const std::vector<int64_t> v
) {
    const size_t H = N / 2;

    auto L = enumerate_all(
        H, K,
        std::vector<int64_t>(w.begin(), w.begin() + H),
        std::vector<int64_t>(v.begin(), v.begin() + H)
    );
    auto R = enumerate_all(
        N - H, K,
        std::vector<int64_t>(w.begin() + H, w.end()),
        std::vector<int64_t>(v.begin() + H, v.end())
    );

    int64_t ans = 0;

    for (size_t j = 0; j <= std::min(K, H); ++j) {
        std::vector<int64_t> comp_v;
        for (const auto &e : R[j]) {
            comp_v.emplace_back(e.second);
        }
        std::sort(comp_v.begin(), comp_v.end());
        comp_v.erase(std::unique(comp_v.begin(), comp_v.end()), comp_v.end());
        for (auto &e : R[j]) {
            e.second = std::lower_bound(comp_v.begin(), comp_v.end(), e.second) - comp_v.begin();
        }
        const size_t m = comp_v.size();

        for (size_t i = 0; i <= std::min(K - j, N - H); ++i) {
            atcoder::fenwick_tree<uint32_t> ft(m);
            auto itR = R[j].begin();
            for (auto itL = L[i].rbegin(); itL != L[i].rend(); ++itL) {
                auto [wsum, vsum] = *itL;
                int64_t maxw = W - wsum;
                for (; itR != R[j].end() and itR->first <= maxw; ++itR) {
                    ft.add(itR->second, 1);
                }

                int64_t maxv = V - vsum;
                std::size_t l = std::lower_bound(comp_v.begin(), comp_v.end(), maxv) - comp_v.begin();

                ans += (itR - R[j].begin()) - ft.sum(0, l);
            }
        }
    }

    return ans;
}

int main() {
    size_t N, K;
    int64_t W, V;
    std::cin >> N >> K >> W >> V;
    std::vector<int64_t> w(N), v(N);
    for (size_t i = 0; i < N; ++i) {
        std::cin >> w[i] >> v[i];
    }
    std::cout << solve(N, K, W, V, w, v) << std::endl;
}