#include <bits/stdc++.h>
using namespace std;
int Day12[] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
int prime100[] = {2,  3,  5,  7,  11, 13, 17, 19, 23, 29, 31, 37,  41, 43,
                  47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103};
template <typename T>
inline bool isLeap(T y) {
  return (y % 400 == 0) || (y % 100 ? y % 4 == 0 : false);
}
template <typename T>
inline T GCD(T a, T b) {
  a = abs(a);
  b = abs(b);
  if (a < b) swap(a, b);
  while (b) {
    a = a % b;
    swap(a, b);
  }
  return a;
}
template <typename T>
inline T LCM(T x, T y) {
  T tp = GCD(x, y);
  if ((x / tp) * 1. * y > 9e18) return 9e18;
  return (x / tp) * y;
}
template <typename T>
inline T BIGMOD(T A, T B, T M = 1000000007) {
  T ret = 1;
  while (B) {
    if (B & 1) ret = (ret * A) % M;
    A = (A * A) % M;
    B = B >> 1;
  }
  return ret;
}
template <typename T>
inline T BigMod(T A, T B, T M) {
  T ret = 1;
  while (B) {
    if (B & 1) ret = (ret * A) % M;
    A = (A * A) % M;
    B = B >> 1;
  }
  return ret;
}
long long int MySqrt(long long int n) {
  long long int p = sqrt(n);
  if ((p + 1) * (p + 1) <= n)
    return p + 1;
  else if (p * p <= n)
    return p;
  else
    return p - 1;
}
long long int MyPow(long long int x, long long int n) {
  if (n == 0)
    return 1;
  else if (n % 2 == 0)
    return MyPow(x * x, n / 2);
  else
    return x * MyPow(x * x, ((n - 1) / 2));
}
long long int dp[50005][505], ans;
int k;
std::vector<int> V[50005];
void dfs(int u, int papa) {
  dp[u][0] = 1;
  for (auto i : V[u]) {
    if (i == papa) continue;
    dfs(i, u);
    for (int j = 1; j <= k; j++) ans += (dp[u][j - 1] * dp[i][k - j]);
    for (int j = 1; j <= k; j++) dp[u][j] += dp[i][j - 1];
  }
}
int main(int argc, char const *argv[]) {
  int n;
  scanf("%d%d", &(n), &(k));
  for (int i = 1; i < n; i++) {
    int x, y;
    scanf("%d%d", &(x), &(y));
    V[x].push_back(y);
    V[y].push_back(x);
  }
  dfs(1, -1);
  printf("%lld\n", ans);
  return 0;
}

### Prompt

Generate a CPP solution to the following problem:

A tree is a connected graph that doesn't contain any cycles.

The distance between two vertices of a tree is the length (in edges) of the shortest path between these vertices.

You are given a tree with n vertices and a positive number k. Find the number of distinct pairs of the vertices which have a distance of exactly k between them. Note that pairs (v, u) and (u, v) are considered to be the same pair.

Input

The first line contains two integers n and k (1 ≤ n ≤ 50000, 1 ≤ k ≤ 500) — the number of vertices and the required distance between the vertices.

Next n - 1 lines describe the edges as "ai bi" (without the quotes) (1 ≤ ai, bi ≤ n, ai ≠ bi), where ai and bi are the vertices connected by the i-th edge. All given edges are different.

Output

Print a single integer — the number of distinct pairs of the tree's vertices which have a distance of exactly k between them.

Please do not use the %lld specifier to read or write 64-bit integers in С++. It is preferred to use the cin, cout streams or the %I64d specifier.

Examples

Input

5 2
1 2
2 3
3 4
2 5


Output

4


Input

5 3
1 2
2 3
3 4
4 5


Output

2

Note

In the first sample the pairs of vertexes at distance 2 from each other are (1, 3), (1, 5), (3, 5) and (2, 4).

### Response

```cpp
#include <bits/stdc++.h>
using namespace std;
int Day12[] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
int prime100[] = {2,  3,  5,  7,  11, 13, 17, 19, 23, 29, 31, 37,  41, 43,
                  47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103};
template <typename T>
inline bool isLeap(T y) {
  return (y % 400 == 0) || (y % 100 ? y % 4 == 0 : false);
}
template <typename T>
inline T GCD(T a, T b) {
  a = abs(a);
  b = abs(b);
  if (a < b) swap(a, b);
  while (b) {
    a = a % b;
    swap(a, b);
  }
  return a;
}
template <typename T>
inline T LCM(T x, T y) {
  T tp = GCD(x, y);
  if ((x / tp) * 1. * y > 9e18) return 9e18;
  return (x / tp) * y;
}
template <typename T>
inline T BIGMOD(T A, T B, T M = 1000000007) {
  T ret = 1;
  while (B) {
    if (B & 1) ret = (ret * A) % M;
    A = (A * A) % M;
    B = B >> 1;
  }
  return ret;
}
template <typename T>
inline T BigMod(T A, T B, T M) {
  T ret = 1;
  while (B) {
    if (B & 1) ret = (ret * A) % M;
    A = (A * A) % M;
    B = B >> 1;
  }
  return ret;
}
long long int MySqrt(long long int n) {
  long long int p = sqrt(n);
  if ((p + 1) * (p + 1) <= n)
    return p + 1;
  else if (p * p <= n)
    return p;
  else
    return p - 1;
}
long long int MyPow(long long int x, long long int n) {
  if (n == 0)
    return 1;
  else if (n % 2 == 0)
    return MyPow(x * x, n / 2);
  else
    return x * MyPow(x * x, ((n - 1) / 2));
}
long long int dp[50005][505], ans;
int k;
std::vector<int> V[50005];
void dfs(int u, int papa) {
  dp[u][0] = 1;
  for (auto i : V[u]) {
    if (i == papa) continue;
    dfs(i, u);
    for (int j = 1; j <= k; j++) ans += (dp[u][j - 1] * dp[i][k - j]);
    for (int j = 1; j <= k; j++) dp[u][j] += dp[i][j - 1];
  }
}
int main(int argc, char const *argv[]) {
  int n;
  scanf("%d%d", &(n), &(k));
  for (int i = 1; i < n; i++) {
    int x, y;
    scanf("%d%d", &(x), &(y));
    V[x].push_back(y);
    V[y].push_back(x);
  }
  dfs(1, -1);
  printf("%lld\n", ans);
  return 0;
}

```