#include "bits/stdc++.h" // Begin Header {{{ using namespace std; #ifndef DEBUG #define dump(...) #endif #define all(x) x.begin(), x.end() #define rep(i, n) for (intmax_t i = 0, i##_limit = (n); i < i##_limit; ++i) #define reps(i, b, e) for (intmax_t i = (b), i##_limit = (e); i <= i##_limit; ++i) #define repr(i, b, e) for (intmax_t i = (b), i##_limit = (e); i >= i##_limit; --i) #define var(Type, ...) Type __VA_ARGS__; input(__VA_ARGS__) constexpr size_t operator""_zu(unsigned long long value) { return value; }; constexpr intmax_t operator""_jd(unsigned long long value) { return value; }; constexpr uintmax_t operator""_ju(unsigned long long value) { return value; }; constexpr int INF = 0x3f3f3f3f; constexpr intmax_t LINF = 0x3f3f3f3f3f3f3f3f_jd; template using MaxHeap = priority_queue, less>; template using MinHeap = priority_queue, greater>; inline void input() {} template inline void input(Head&& head, Tail&&... tail) { cin >> head; input(forward(tail)...); } template inline void input(vector &vec) { for (auto &e: vec) { cin >> e; } } template inline void input(vector> &mat) { for (auto &vec: mat) { input(vec); } } inline void print() { cout << "\n"; } template inline void print(Head&& head, Tail&&... tail) { cout << head; if (sizeof...(tail)) { cout << " "; } print(forward(tail)...); } template inline ostream& operator<<(ostream &os, const vector &vec) { static constexpr const char *delim[] = {" ", ""}; for (const auto &e: vec) { os << e << delim[&e == &vec.back()]; } return os; } template inline vector makeVector(const T &initValue, size_t sz) { return vector(sz, initValue); } template inline auto makeVector(const T &initValue, size_t sz, Args... args) { return vector(initValue, args...))>(sz, makeVector(initValue, args...)); } template class FixPoint : Func { public: explicit constexpr FixPoint(Func&& f) noexcept : Func(forward(f)) {} template constexpr decltype(auto) operator()(Args&&... args) const { return Func::operator()(*this, std::forward(args)...); } }; template static inline constexpr decltype(auto) makeFixPoint(Func&& f) noexcept { return FixPoint{forward(f)}; } template inline bool chmax(T &a, const T &b) noexcept { return b > a && (a = b, true); } template inline bool chmin(T &a, const T &b) noexcept { return b < a && (a = b, true); } template inline T diff(const T &a, const T &b) noexcept { return a < b ? b - a : a - b; } // End Header }}} // Edge {{{ template struct Edge { size_t from, to; Weight weight; Edge() {} Edge(size_t from, size_t to, Weight weight = 1) : from(from), to(to), weight(weight) {} bool operator<(const Edge &rhs) const { return weight < rhs.weight; } bool operator>(const Edge &rhs) const { return weight > rhs.weight; } operator size_t() const { return to; } }; // }}} // Graph {{{ template class Graph : public vector>> { using graph = vector>>; public: Graph() {} Graph(const size_t V) : graph(V) {} void connect(size_t from, size_t to, Weight weight = 1) { (*this)[from].emplace_back(from, to, weight); } friend ostream& operator<<(ostream &strm, const Graph &G) { for (size_t v = 0; v < G.size(); ++v) { strm << '[' << setw(2) << v << ']'; for (const auto &e: G[v]) { strm << ' ' << setw(2) << e.to; } strm << '\n'; } return strm; } }; // }}} int main() { ios_base::sync_with_stdio(false); cin.tie(nullptr); var(size_t, N, K); Graph G(N); rep(i, N - 1) { var(size_t, a, b); a--, b--; G.connect(a, b); G.connect(b, a); } if (K > N) { return print(-1), 0; } vector seen(N); const auto dfs = makeFixPoint([&](auto dfs, size_t cur) -> void { seen[cur] = true; for (const auto e: G[cur]) { if (!seen[e.to]) { dfs(e.to); } } }); dfs(0); size_t connectedCnt = 0; rep(v, N) { connectedCnt += seen[v]; } if (connectedCnt >= K) { print(K - 1); } else { print(-1); } return 0; }