// #define _NDEBUG
#define _CRT_SECURE_NO_WARNINGS
#define _USE_MATH_DEFINES
#include "bits/stdc++.h"
#include <unordered_map>
#include <unordered_set>
#ifdef _MSC_VER
#include <ppl.h>
#include <concurrent_vector.h>
#include <filesystem>
//#include <boost/multiprecision/cpp_dec_float.hpp>
//#include <boost/multiprecision/cpp_int.hpp>
//#include <boost/rational.hpp>
#include <opencv2/core.hpp>
#include <opencv2/imgproc.hpp>
#include <opencv2/highgui.hpp>
//#else
//#include <omp.h>
#endif



/* type */
using uint = unsigned; using ll = long long; using ull = unsigned long long; using pii = std::pair<int, int>; using pll = std::pair<ll, ll>;
/* io */
template <typename _KTy, typename _Ty> std::ostream& operator << (std::ostream& o, const std::pair<_KTy, _Ty>& m) { o << "[" << m.first << ", " << m.second << "]"; return o; }
template <typename _KTy, typename _Ty> std::ostream& operator << (std::ostream& o, const std::map<_KTy, _Ty>& m) { if (m.empty()) { o << "[]"; return o; } o << "[" << *m.begin(); for (auto itr = ++m.begin(); itr != m.end(); itr++) { o << ", " << *itr; } o << "]"; return o; }
template <typename _KTy, typename _Ty> std::ostream& operator << (std::ostream& o, const std::unordered_map<_KTy, _Ty>& m) { if (m.empty()) { o << "[]"; return o; } o << "[" << *m.begin(); for (auto itr = ++m.begin(); itr != m.end(); itr++) { o << ", " << *itr; } o << "]"; return o; }
template <typename _Ty> std::ostream& operator << (std::ostream& o, const std::vector<_Ty>& v) { if (v.empty()) { o << "[]"; return o; } o << "[" << v.front(); for (auto itr = ++v.begin(); itr != v.end(); itr++) { o << ", " << *itr; } o << "]"; return o; }
template <typename _Ty> std::ostream& operator << (std::ostream& o, const std::deque<_Ty>& v) { if (v.empty()) { o << "[]"; return o; } o << "[" << v.front(); for (auto itr = ++v.begin(); itr != v.end(); itr++) { o << ", " << *itr; } o << "]"; return o; }
template <typename _Ty> std::ostream& operator << (std::ostream& o, const std::set<_Ty>& s) { if (s.empty()) { o << "[]"; return o; } o << "[" << *(s.begin()); for (auto itr = ++s.begin(); itr != s.end(); itr++) { o << ", " << *itr; } o << "]"; return o; }
template <typename _Ty> std::ostream& operator << (std::ostream& o, const std::unordered_set<_Ty>& s) { if (s.empty()) { o << "[]"; return o; } o << "[" << *(s.begin()); for (auto itr = ++s.begin(); itr != s.end(); itr++) { o << ", " << *itr; }	o << "]"; return o; }
template <typename _Ty> std::ostream& operator << (std::ostream& o, const std::stack<_Ty>& s) { if (s.empty()) { o << "[]"; return o; } std::stack<_Ty> t(s); o << "[" << t.top(); t.pop(); while (!t.empty()) { o << ", " << t.top(); t.pop(); } o << "]";	return o; }
template <typename _Ty> std::ostream& operator << (std::ostream& o, const std::list<_Ty>& l) { if (l.empty()) { o << "[]"; return o; } o << "[" << l.front(); for (auto itr = ++l.begin(); itr != l.end(); ++itr) { o << ", " << *itr; } o << "]"; return o; }
template <typename _KTy, typename _Ty> std::istream& operator >> (std::istream& is, std::pair<_KTy, _Ty>& m) { is >> m.first >> m.second; return is; }
template <typename _Ty> std::istream& operator >> (std::istream& is, std::vector<_Ty>& v) { for (size_t t = 0; t < v.size(); t++) is >> v[t]; return is; }
template <typename _Ty> std::istream& operator >> (std::istream& is, std::deque<_Ty>& v) { for (size_t t = 0; t < v.size(); t++) is >> v[t]; return is; }
namespace aux { // print tuple
  template<typename Ty, unsigned N, unsigned L> struct tp { static void print(std::ostream& os, const Ty& v) { os << std::get<N>(v) << ", "; tp<Ty, N + 1, L>::print(os, v); } };
  template<typename Ty, unsigned N> struct tp<Ty, N, N> { static void print(std::ostream& os, const Ty& v) { os << std::get<N>(v); } };
}
template<typename... Tys> std::ostream& operator<<(std::ostream& os, const std::tuple<Tys...>& t) { os << "["; aux::tp<std::tuple<Tys...>, 0, sizeof...(Tys) - 1>::print(os, t); os << "]"; return os; }
/* fill */
template<typename A, size_t N, typename T>
void Fill(A(&array)[N], const T& val) {
  std::fill((T*)array, (T*)(array + N), val);
}
/* format */
template <typename ... Args>
std::string format(const std::string& fmt, Args ... args) {
  size_t len = std::snprintf(nullptr, 0, fmt.c_str(), args ...);
  std::vector<char> buf(len + 1);
  std::snprintf(&buf[0], len + 1, fmt.c_str(), args ...);
  return std::string(&buf[0], &buf[0] + len);
}
/* dump */
#define DUMPOUT std::cerr
#define dump(...) do{DUMPOUT<<"  ";DUMPOUT<<#__VA_ARGS__<<" :[DUMP - "<<__LINE__<<":"<<__FUNCTION__<<"]"<<std::endl;DUMPOUT<<"    ";dump_func(__VA_ARGS__);}while(0);
void dump_func() { DUMPOUT << std::endl; }
template <class Head, class... Tail> void dump_func(Head&& head, Tail&&... tail) { DUMPOUT << head; if (sizeof...(Tail) == 0) { DUMPOUT << " "; } else { DUMPOUT << ", "; } dump_func(std::move(tail)...); }
/* timer */
class Timer {
public:
  double t = 0;
  Timer() { reset(); }
  static double time() {
#ifdef _MSC_VER
    return __rdtsc() / 2.8e9;
#else
    unsigned long long a, d;
    __asm__ volatile("rdtsc"
      : "=a"(a), "=d"(d));
    return (d << 32 | a) / 2.8e9;
#endif
  }
  //void measure() { t = time() - t; }
  void reset() { t = time(); }
  double elapsedMs() { return (time() - t) * 1000.0; }
} timer;
/* rand */
struct Xorshift {
  uint64_t x = 88172645463325252LL;
  unsigned next_int() {
    x = x ^ (x << 7);
    return x = x ^ (x >> 9);
  }
  unsigned next_int(unsigned mod) {
    x = x ^ (x << 7);
    x = x ^ (x >> 9);
    return x % mod;
  }
  unsigned next_int(unsigned l, unsigned r) {
    x = x ^ (x << 7);
    x = x ^ (x >> 9);
    return x % (r - l + 1) + l;
  }
  double next_double() {
    return double(next_int()) / UINT_MAX;
  }
} rnd;
/* shuffle */
template<typename T>
void shuffle_vector(std::vector<T>& v, Xorshift& rnd) {
  int n = v.size();
  for (int i = n - 1; i >= 1; i--) {
    int r = rnd.next_int(i);
    std::swap(v[i], v[r]);
  }
}



using namespace std;

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);

  ll N, X;
  cin >> N >> X;
  vector<ll> S(N);
  cin >> S;

  ll Y = 0;
  for (ll n = 0; n < N; n++) Y += X - S[n];

  for (ll n = 0; n < N; n++) {
    if (S[n] % 2 == 0 && Y + S[n] / 2 == X) {
      cout << S[n] / 2 << endl;
      return 0;
    }
  }

  return 0;
}