37d77db5.cpp

#include <bits/stdc++.h>
#define watch(x) std::cout << "$ LINE @" << __LINE__ << " FUNC @" << __FUNCTION__ << "\n$ " \
                           << (#x) << ": " << x << std::endl

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> pii;

template <typename Tp>
inline void read(Tp &x)
{
    static char c;
    static bool neg;
    x = 0, c = getchar(), neg = false;
    for (; !isdigit(c); c = getchar())
    {
        if (c == '-')
        {
            neg = true;
        }
    }
    for (; isdigit(c); c = getchar())
    {
        x = x * 10 + c - '0';
    }
    if (neg)
    {
        x = -x;
    }
}

const int N = 4000 + 5;

int n, k;

int head[N], E = 0;
struct Edge
{
    int to, next;
} e[N * 2];
inline void addEdge(int u, int v)
{
    e[++E] = (Edge){v, head[u]};
    head[u] = E;
}

bitset<N> valid[N];

bitset<N> st;

int dep[N];

void dfs(int u, int fa)
{
    dep[u] = dep[fa] + 1;
    for (int i = head[u], v; v = e[i].to, i; i = e[i].next)
    {
        if (v != fa)
        {
            dfs(v, u);
        }
    }
}

int main()
{
    read(n), read(k);
    for (int i = 1, u, v; i < n; ++i)
    {
        read(u), read(v);
        addEdge(u, v);
        addEdge(v, u);
    }
    dep[0] = -1;
    for (int i = 1; i <= n; ++i)
    {
        dfs(i, 0);
        for (int j = i + 1; j <= n; ++j)
        {
            if (dep[j] <= k)
            {
                valid[i].set(j);
            }
        }
    }
    ll ans = 0;
    for (int a = 1; a <= n; ++a)
    {
        for (int c = a + 1; c <= n; ++c)
        {
            if (valid[a].test(c) && a != c)
            {
                ans += (valid[a] & valid[c]).count();
            }
        }
    }
    printf("%lld\n", ans * 6);
}