#include <bits/stdc++.h>
using namespace std;
const int N = 5005;
int n, k, dist[N][N];
vector<int> g[N], vec;
void dfs(int v, int r, int p = -1){
for (int u : g[v]){
if (u == p) continue;
dist[r][u] = dist[r][v] + 1;
dfs(u, r, v);
}
}
int main(){
cin >> n >> k;
for (int i = 0; i < n - 1; i ++){
int u, v;
cin >> u >> v;
g[u].push_back(v);
g[v].push_back(u);
}
for (int r = 1; r <= n; r ++)
dfs(r, r);
for (int i = 1; i <= n; i ++){
vec.clear();
for (int v = 1; v <= n; v ++)
if (dist[i][v] % k == 0)
vec.push_back(v);
bool bad_root = 0;
for (int u = 1; u <= n; u ++){
for (int v = 1; v <= n; v ++){
if (dist[u][v] != k - 1) continue;
int cnt = 0;
for (int x : vec)
cnt += (dist[u][v] == dist[u][x] + dist[x][v]);
bad_root |= (cnt != 1);
}
}
if (bad_root) continue;
cout << "YES" << endl << 0 << endl;
return 0;
}
cout << "NO" << endl << 0 << endl;
return 0;
}
