//#define NDEBUG
#include <algorithm>
#include <cstddef>
#include <cstdint>
#include <iostream>
#include <vector>

namespace n91 {

  using i8 = std::int_fast8_t;
  using i32 = std::int_fast32_t;
  using i64 = std::int_fast64_t;
  using u8 = std::uint_fast8_t;
  using u32 = std::uint_fast32_t;
  using u64 = std::uint_fast64_t;
  using isize = std::ptrdiff_t;
  using usize = std::size_t;

  struct rep {
    struct itr {
      usize i;
      constexpr itr(const usize i) noexcept : i(i) {}
      void operator++() noexcept { ++i; }
      constexpr usize operator*() const noexcept { return i; }
      constexpr bool operator!=(const itr x) const noexcept { return i != x.i; }
    };
    const itr f, l;
    constexpr rep(const usize f, const usize l) noexcept
      : f(std::min(f, l)), l(l) {}
    constexpr auto begin() const noexcept { return f; }
    constexpr auto end() const noexcept { return l; }
  };
  struct revrep {
    struct itr {
      usize i;
      constexpr itr(const usize i) noexcept : i(i) {}
      void operator++() noexcept { --i; }
      constexpr usize operator*() const noexcept { return i; }
      constexpr bool operator!=(const itr x) const noexcept { return i != x.i; }
    };
    const itr f, l;
    constexpr revrep(const usize f, const usize l) noexcept
      : f(l - 1), l(std::min(f, l) - 1) {}
    constexpr auto begin() const noexcept { return f; }
    constexpr auto end() const noexcept { return l; }
  };
  template <class T> auto md_vec(const usize n, const T& value) {
    return std::vector<T>(n, value);
  }
  template <class... Args> auto md_vec(const usize n, Args... args) {
    return std::vector<decltype(md_vec(args...))>(n, md_vec(args...));
  }
  template <class T> constexpr T difference(const T& a, const T& b) noexcept {
    return a < b ? b - a : a - b;
  }
  template <class T> void chmin(T& a, const T& b) noexcept {
    if (b < a)
      a = b;
  }
  template <class T> void chmax(T& a, const T& b) noexcept {
    if (a < b)
      a = b;
  }
  template <class T> T scan() {
    T ret;
    std::cin >> ret;
    return ret;
  }

} // namespace n91

#include <algorithm>
#include <iostream>
#include <limits>
#include <utility>

namespace n91 {

  void main_() {
    while (true) {

      static constexpr u64 Inf = std::numeric_limits<u64>::max() / 20;
      const usize n{ scan<usize>() };
      const usize m{ scan<usize>() };
      const usize l{ scan<usize>() };
      const usize start{ scan<usize>() - 1 };
      const u64 t{ scan<usize>() };

      if (n == 0) {
        return;
      }

      auto d = md_vec(n, n, Inf);
      for (const auto i : rep(0, n)) {
        d[i][i] = 0;
      }
      for (const auto i : rep(0, m)) {
        const usize a{ scan<usize>() - 1 };
        const usize b{ scan<usize>() - 1 };
        const u64 c{ scan<u64>() };
        d[a][b] = c;
        d[b][a] = c;
      }
      for (const auto j : rep(0, n)) {
        for (const auto i : rep(0, n)) {
          for (const auto k : rep(0, n)) {
            chmin(d[i][k], d[i][j] + d[j][k]);
          }
        }
      }
      struct siro_t {
        usize j;
        u64 e;
      };
      std::vector<siro_t> siro(l);
      for (auto& e : siro) {
        e.j = scan<usize>() - 1;
        e.e = scan<u64>();
      }
      siro.push_back({ start, 0 });
      auto dp = md_vec(l + 1, 1 << l, Inf);
      dp[l][0] = 0;
      for (const auto s : rep(0, 1 << l)) {
        for (const auto i : rep(0, l + 1)) {
          for (const auto k : rep(0, l)) {
            chmin(dp[k][s | 1 << k],
              dp[i][s] + d[siro[i].j][siro[k].j] + siro[k].e);
          }
        }
      }
      usize ans = 0;
      for (const auto i : rep(0, l)) {
        for (const auto s : rep(0, 1 << l)) {
          if (dp[i][s] + d[siro[i].j][start] <= t) {
            usize cnt = 0;
            for (const auto k : rep(0, l)) {
              if (s >> k & 1) {
                ++cnt;
              }
            }
            chmax(ans, cnt);
          }
        }
      }
      std::cout << ans << std::endl;
    }
  }

} // namespace n91

int main() {
  n91::main_();
  return 0;
}



Measured memory_bytes: 12712