Problem: The Main Martian Tree grows on Mars. It is a binary tree (a rooted tree, with no more than two sons at each vertex) with n vertices, where the root vertex has the number 1. Its fruits are the Main Martian Fruits. It's summer now, so this tree does not have any fruit yet.

Autumn is coming soon, and leaves and branches will begin to fall off the tree. It is clear, that if a vertex falls off the tree, then its entire subtree will fall off too. In addition, the root will remain on the tree. Formally: the tree will have some connected subset of vertices containing the root.

After that, the fruits will grow on the tree (only at those vertices which remain). Exactly x fruits will grow in the root. The number of fruits in each remaining vertex will be not less than the sum of the numbers of fruits in the remaining sons of this vertex. It is allowed, that some vertices will not have any fruits.

Natasha wondered how many tree configurations can be after the described changes. Since this number can be very large, output it modulo 998244353.

Two configurations of the resulting tree are considered different if one of these two conditions is true:

  * they have different subsets of remaining vertices;
  * they have the same subset of remaining vertices, but there is a vertex in this subset where they have a different amount of fruits.

Input

The first line contains two integers: n and x (1 ≤ n ≤ 10^5, 0 ≤ x ≤ 10^{18}) — the size of the tree and the number of fruits in the root.

The i-th of the following (n-1) lines contains two integers a_i and b_i (1 ≤ a_i, b_i ≤ n) — vertices connected by the i-th edge of the tree.

It is guaranteed that the input data describes a correct binary tree with the root at the vertex 1.

Output

Print one number — the number of configurations of the resulting tree modulo 998244353.

Examples

Input

3 2
1 2
1 3


Output

13


Input

2 5
1 2


Output

7


Input

4 10
1 2
1 3
3 4


Output

441

Note

Consider the first example. <image>

There are 2 fruits at the vertex 1. The following 13 options are possible:

  * there is no vertex 2, there is no vertex 3; <image>
  * there is no vertex 2, there are no fruits at the vertex 3; <image>
  * there is no vertex 2, there is 1 fruit at the vertex 3; <image>
  * there is no vertex 2, there are 2 fruits at the vertex 3; <image>
  * there are no fruits at the vertex 2, there is no vertex 3; <image>
  * there are no fruits at the vertex 2, there are no fruits at the vertex 3; <image>
  * there are no fruits at the vertex 2, there is 1 fruit at the vertex 3; <image>
  * there are no fruits at the vertex 2, there are 2 fruits at the vertex 3; <image>
  * there is 1 fruit at the vertex 2, there is no vertex 3; <image>
  * there is 1 fruit at the vertex 2, there are no fruits at the vertex 3; <image>
  * there is 1 fruit at the vertex 2, there is 1 fruit at the vertex 3; <image>
  * there are 2 fruits at the vertex 2, there is no vertex 3; <image>
  * there are 2 fruits at the vertex 2, there are no fruits at the vertex 3. <image>



Consider the second example. There are 5 fruits at the vertex 1. The following 7 options are possible:

  * there is no vertex 2;
  * there are no fruits at the vertex 2;
  * there is 1 fruit at the vertex 2;
  * there are 2 fruits at the vertex 2;
  * there are 3 fruits at the vertex 2;
  * there are 4 fruits at the vertex 2;
  * there are 5 fruits at the vertex 2.

Solution (in CPP):

Solution:
#include <bits/stdc++.h>
using namespace std;
inline void read(int &x) {
  int v = 0, f = 1;
  char c = getchar();
  while (!isdigit(c) && c != '-') c = getchar();
  if (c == '-')
    f = -1;
  else
    v = (c & 15);
  while (isdigit(c = getchar())) v = (v << 1) + (v << 3) + (c & 15);
  x = v * f;
}
inline void read(long long &x) {
  long long v = 0ll, f = 1ll;
  char c = getchar();
  while (!isdigit(c) && c != '-') c = getchar();
  if (c == '-')
    f = -1;
  else
    v = (c & 15);
  while (isdigit(c = getchar())) v = (v << 1) + (v << 3) + (c & 15);
  x = v * f;
}
inline void readc(char &x) {
  char c;
  while (((c = getchar()) == ' ') || c == '\n')
    ;
  x = c;
}
const int maxn = 262144;
const int mod = 998244353, _k = 119, _b = 23, _g = 3;
inline void inc(int &x, int y) {
  x += y;
  if (x >= mod) x -= mod;
}
inline void dec(int &x, int y) {
  x -= y;
  if (x < 0) x += mod;
}
inline int qp(int x, int y) {
  int z = 1;
  while (y) {
    if (y & 1) z = 1ll * z * x % mod;
    y >>= 1;
    x = 1ll * x * x % mod;
  }
  return z;
}
namespace polynomial {
namespace basic {
int fac[maxn + 5], inv[maxn + 5], first[maxn + 5], lg[maxn + 5], pw[maxn + 5],
    w[maxn + 5], iw[maxn + 5];
bool tag = 0;
inline void init() {
  tag = 1;
  int i;
  for ((i) = (2); (i) <= (maxn); (i)++) lg[i] = lg[i >> 1] + 1;
  pw[0] = 1;
  for (((i)) = (1); ((i)) <= ((lg[maxn])); ((i))++) pw[i] = pw[i - 1] * 2;
  fac[0] = fac[1] = inv[1] = first[0] = first[1] = 1;
  for ((i) = (2); (i) <= (maxn); (i)++) {
    fac[i] = 1ll * fac[i - 1] * i % mod;
    inv[i] = (mod - mod / i) * 1ll * inv[mod % i] % mod;
    first[i] = 1ll * first[i - 1] * inv[i] % mod;
  }
  w[0] = 1;
  w[1] = qp(_g, (mod - 1) / maxn);
  for ((i) = (2); (i) <= (maxn); (i)++) w[i] = 1ll * w[i - 1] * w[1] % mod;
  iw[maxn] = qp(w[maxn], mod - 2);
  for (((i)) = (((int)(maxn)) - 1); ((i)) >= (0); ((i))--)
    iw[i] = 1ll * iw[i + 1] * w[1] % mod;
}
int rev[maxn + 5], a[maxn + 5], b[maxn + 5];
inline int getrev(int x) {
  if (!tag) init();
  int i, s = 1;
  while (s < x) s *= 2;
  rev[0] = 0;
  for (((i)) = (1); ((i)) <= ((s - 1)); ((i))++)
    rev[i] = ((rev[i >> 1] >> 1) | ((i & 1) << (lg[s] - 1)));
  return s;
}
inline void ntt(int *a, int n, int *w) {
  if (!tag) init();
  int i, j, k;
  for (((i)) = (0); ((i)) <= (((int)(n)) - 1); ((i))++)
    if (rev[i] < i) swap(a[i], a[rev[i]]);
  for (i = 1; i < n; i <<= 1) {
    int ys = maxn / i / 2;
    for (j = 0; j < n; j += i + i) {
      int *t = w;
      for (((k)) = (0); ((k)) <= (((int)(i)) - 1); ((k))++) {
        int x = a[j + k], y = 1ll * a[j + k + i] * (*t) % mod;
        a[j + k] = x + y;
        if (a[j + k] >= mod) a[j + k] -= mod;
        a[j + k + i] = x - y;
        if (a[j + k + i] < 0) a[j + k + i] += mod;
        t += ys;
      }
    }
  }
}
inline vector<int> mul(const vector<int> &aa, const vector<int> &bb) {
  vector<int> ans;
  long long br = 1ll * aa.size() * bb.size(),
            ft =
                1ll * (aa.size() + bb.size()) * lg[aa.size() + bb.size()] * 10 +
                100;
  if (br < ft) {
    while (ans.size() + 1 < aa.size() + bb.size()) ans.push_back(0);
    int i, j;
    for (((i)) = (0); ((i)) <= (((int)(aa.size())) - 1); ((i))++)
      for (((j)) = (0); ((j)) <= (((int)(bb.size())) - 1); ((j))++)
        inc(ans[i + j], 1ll * aa[i] * bb[j] % mod);
  } else {
    int len = getrev(aa.size() + bb.size()), i;
    for (((i)) = (0); ((i)) <= (((int)(len)) - 1); ((i))++) a[i] = b[i] = 0;
    for (((i)) = (0); ((i)) <= (((int)(aa.size())) - 1); ((i))++) a[i] = aa[i];
    for (((i)) = (0); ((i)) <= (((int)(bb.size())) - 1); ((i))++) b[i] = bb[i];
    ntt(a, len, w);
    ntt(b, len, w);
    for (((i)) = (0); ((i)) <= (((int)(len)) - 1); ((i))++)
      a[i] = 1ll * a[i] * b[i] % mod;
    ntt(a, len, iw);
    int inv = qp(len, mod - 2);
    for (((i)) = (0); ((i)) <= (((int)(len)) - 1); ((i))++)
      ans.push_back(1ll * a[i] * inv % mod);
  }
  while (!ans.empty() && !ans.back()) ans.pop_back();
  return ans;
}
inline vector<int> mul2(const vector<int> &aa, const vector<int> &bb) {
  int len = getrev(aa.size() + aa.size() + bb.size()), i;
  for (((i)) = (0); ((i)) <= (((int)(len)) - 1); ((i))++) a[i] = b[i] = 0;
  for (((i)) = (0); ((i)) <= (((int)(aa.size())) - 1); ((i))++) a[i] = aa[i];
  for (((i)) = (0); ((i)) <= (((int)(bb.size())) - 1); ((i))++) b[i] = bb[i];
  ntt(a, len, w);
  ntt(b, len, w);
  for (((i)) = (0); ((i)) <= (((int)(len)) - 1); ((i))++)
    a[i] = 1ll * a[i] * b[i] % mod * a[i] % mod;
  ntt(a, len, iw);
  vector<int> ans;
  int inv = qp(len, mod - 2);
  for (((i)) = (0); ((i)) <= (((int)(len)) - 1); ((i))++)
    ans.push_back(1ll * a[i] * inv % mod);
  while (!ans.empty() && !ans.back()) ans.pop_back();
  return ans;
}
};  // namespace basic
struct poly {
  vector<int> v;
  inline void clear() { v.clear(); }
  inline int size() { return v.size(); }
  inline bool empty() { return v.empty(); }
  inline int back() { return v.back(); }
  inline void pop_back() { v.pop_back(); }
  inline void push_back(int x) { v.push_back(x); }
  inline poly operator+(const poly &x) const {
    vector<int> s;
    int i;
    for (i = 0; i < x.v.size() || i < v.size(); i++) {
      int t = 0;
      if (i < v.size()) inc(t, v[i]);
      if (i < x.v.size()) inc(t, x.v[i]);
      s.push_back(t);
    }
    return (poly){s};
  }
  inline poly operator-(const poly &x) const {
    vector<int> s;
    int i;
    for (i = 0; i < x.v.size() || i < v.size(); i++) {
      int t = 0;
      if (i < v.size()) inc(t, v[i]);
      if (i < x.v.size()) dec(t, x.v[i]);
      s.push_back(t);
    }
    return (poly){s};
  }
  inline poly operator*(const int &x) const {
    vector<int> s;
    int i;
    for (i = 0; i < v.size(); i++) s.push_back(1ll * x * v[i] % mod);
    return (poly){s};
  }
  inline poly operator*(const poly &x) const {
    return (poly){basic::mul(v, x.v)};
  }
  inline void size_down(int x) {
    while (v.size() > x) v.pop_back();
  }
  inline void size_up(int x) {
    while (v.size() < x) v.push_back(0);
  }
  inline void resize(int x) {
    size_down(x);
    size_up(x);
  }
  inline int &operator[](const int &x) {
    if (v.size() <= x) size_up(x + 1);
    return v[x];
  }
};
};  // namespace polynomial
using namespace polynomial;
int n, i, j, t, fa[100005], sz[100005], tp[100005], son[100005];
vector<int> e[100005];
void dfs1(int x, int p) {
  fa[x] = p;
  sz[x] = 1;
  for (__typeof((e[x]).begin()) it = (e[x]).begin(); it != (e[x]).end(); it++) {
    if (*it == p) continue;
    dfs1(*it, x);
    sz[x] += sz[*it];
    if (!son[x] || sz[son[x]] < sz[*it]) son[x] = *it;
  }
}
vector<poly> v;
poly one, poly_x;
pair<poly, poly> calc(int l, int r) {
  if (l == r) return make_pair(v[l] + one, v[l]);
  int mid = (l + r) / 2;
  pair<poly, poly> sl = calc(l, mid), sr = calc(mid + 1, r);
  return make_pair((sl.first - one) * sr.second + sr.first,
                   sl.second * sr.second);
}
poly solve(int x) {
  int t = x;
  vector<poly> vv;
  while (t) {
    bool f = 0;
    for (__typeof((e[t]).begin()) it = (e[t]).begin(); it != (e[t]).end(); it++)
      if (*it != fa[t] && *it != son[t]) {
        vv.push_back(solve(*it) * poly_x);
        f = 1;
      }
    if (!f) {
      poly p;
      p.push_back(0);
      p.push_back(1);
      vv.push_back(p);
    }
    t = son[t];
  }
  reverse((vv).begin(), (vv).end());
  v = vv;
  poly res = calc(0, v.size() - 1).first;
  return res;
}
int main() {
  one.push_back(1);
  poly_x.push_back(0);
  poly_x.push_back(1);
  long long _;
  read(n);
  read(_);
  t = _ % mod;
  for (((i)) = (1); ((i)) <= ((n - 1)); ((i))++) {
    int x, y;
    read(x);
    read(y);
    e[x].push_back(y);
    e[y].push_back(x);
  }
  dfs1(1, 0);
  poly res = solve(1);
  int coef = 1, ans = 0;
  for (((i)) = (1); ((i)) <= ((n)); ((i))++) {
    ans = (ans + 1ll * res[i] * coef) % mod;
    coef = 1ll * coef * qp(i, mod - 2) % mod * (t + i) % mod;
  }
  cout << ans << endl;
  return 0;
}