func_code_string: #include <bits/stdc++.h>   using namespace std;   template <typename T, typename U>   inline void smin(T &a, const U &b) {     if (a > b) a = b;   }   template <typename T, typename U>   inline void smax(T &a, const U &b) {     if (a < b) a = b;   }   template <class T>   inline void gn(T &first) {     char c, sg = 0;     while (c = getchar(), (c >  9  || c <  0 ) && c !=  - )       ;     for ((c ==  -  ? sg = 1, c = getchar() : 0), first = 0; c >=  0  && c <=  9 ;          c = getchar())       first = (first << 1) + (first << 3) + c -  0 ;     if (sg) first = -first;   }   template <class T1, class T2>   inline void gn(T1 &x1, T2 &x2) {     gn(x1), gn(x2);   }   int power(int a, int b, int m, int ans = 1) {     for (; b; b >>= 1, a = 1LL * a * a % m)       if (b & 1) ans = 1LL * ans * a % m;     return ans;   }   const int mod = 1000000007;   vector<int> adj[111];   int dp[111][50], k;   int tmp[50];   inline void add(int &a, long long b) { a = (a + b) % mod; }   void dfs(int u, int f = 0) {     dp[u][25 + k] = 1;     dp[u][25 - 1] = 1;     for (int v : adj[u]) {       if (v == f) continue;       dfs(v, u);       for (int i = -k; i <= k; i++)         tmp[25 + i] = dp[u][25 + i], dp[u][25 + i] = 0;       for (int i = -k; i <= k; i++)         for (int j = -k; j <= k; j++) {           if (i + j >= 0)             add(dp[u][25 + max(i, j - 1)],                 (long long)tmp[25 + i] * dp[v][25 + j]);           else             add(dp[u][25 + min(i, j - 1)],                 (long long)tmp[25 + i] * dp[v][25 + j]);         }     }   }   int main() {     int n;     cin >> n >> k;     for (int i = 1; i < n; i++) {       int u, v;       gn(u, v);       adj[u].push_back(v);       adj[v].push_back(u);     }     dfs(1);     int ans = 0;     for (int i = 0; i <= k; i++) add(ans, dp[1][25 + i]);     cout << ans << endl;     return 0;   }   