#define MOD_TYPE 2

#include <bits/stdc++.h>
using namespace std;

#include <atcoder/all>
//#include <atcoder/modint>
//#include <atcoder/lazysegtree>
//#include <atcoder/segtree>

using namespace atcoder;

#if 0
#include <boost/multiprecision/cpp_dec_float.hpp>
#include <boost/multiprecision/cpp_int.hpp>
using Int = boost::multiprecision::cpp_int;
using lld = boost::multiprecision::cpp_dec_float_100;
#endif

#if 0
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tag_and_trait.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/rope>
using namespace __gnu_pbds;
using namespace __gnu_cxx;
template <typename T>
using extset =
    tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
#endif

#if 1
#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#endif

#pragma region Macros

using ll = long long int;
using ld = long double;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using pld = pair<ld, ld>;
template <typename Q_type>
using smaller_queue = priority_queue<Q_type, vector<Q_type>, greater<Q_type>>;

#if MOD_TYPE == 1
constexpr ll MOD = ll(1e9 + 7);
#else
#if MOD_TYPE == 2
constexpr ll MOD = 998244353;
#else
constexpr ll MOD = 1000003;
#endif
#endif

using mint = static_modint<MOD>;
constexpr int INF = (int)1e9 + 10;
constexpr ll LINF = (ll)4e18;
constexpr double PI = acos(-1.0);
constexpr double EPS = 1e-11;
constexpr int Dx[] = {0, 0, -1, 1, -1, 1, -1, 1, 0};
constexpr int Dy[] = {1, -1, 0, 0, -1, -1, 1, 1, 0};

#define REP(i, m, n) for (ll i = m; i < (ll)(n); ++i)
#define rep(i, n) REP(i, 0, n)
#define REPI(i, m, n) for (int i = m; i < (int)(n); ++i)
#define repi(i, n) REPI(i, 0, n)
#define YES(n) cout << ((n) ? "YES" : "NO") << "\n"
#define Yes(n) cout << ((n) ? "Yes" : "No") << "\n"
#define possible(n) cout << ((n) ? "possible" : "impossible") << "\n"
#define Possible(n) cout << ((n) ? "Possible" : "Impossible") << "\n"
#define all(v) v.begin(), v.end()
#define NP(v) next_permutation(all(v))
#define dbg(x) cerr << #x << ":" << x << "\n";
#define UNIQUE(v) v.erase(unique(all(v)), v.end())

struct io_init {
  io_init() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cout << setprecision(30) << setiosflags(ios::fixed);
  };
} io_init;
template <typename T>
inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T>
inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
inline ll floor(ll a, ll b) {
  if (b < 0) a *= -1, b *= -1;
  if (a >= 0) return a / b;
  return -((-a + b - 1) / b);
}
inline ll ceil(ll a, ll b) { return floor(a + b - 1, b); }
template <typename A, size_t N, typename T>
inline void Fill(A (&array)[N], const T &val) {
  fill((T *)array, (T *)(array + N), val);
}
template <typename T>
vector<T> compress(vector<T> &v) {
  vector<T> val = v;
  sort(all(val)), val.erase(unique(all(val)), val.end());
  for (auto &&vi : v) vi = lower_bound(all(val), vi) - val.begin();
  return val;
}
template <typename T, typename U>
constexpr istream &operator>>(istream &is, pair<T, U> &p) noexcept {
  is >> p.first >> p.second;
  return is;
}
template <typename T, typename U>
constexpr ostream &operator<<(ostream &os, pair<T, U> p) noexcept {
  os << p.first << " " << p.second;
  return os;
}
ostream &operator<<(ostream &os, mint m) {
  os << m.val();
  return os;
}
ostream &operator<<(ostream &os, modint m) {
  os << m.val();
  return os;
}
template <typename T>
constexpr istream &operator>>(istream &is, vector<T> &v) noexcept {
  for (int i = 0; i < v.size(); i++) is >> v[i];
  return is;
}
template <typename T>
constexpr ostream &operator<<(ostream &os, vector<T> &v) noexcept {
  for (int i = 0; i < v.size(); i++)
    os << v[i] << (i + 1 == v.size() ? "" : " ");
  return os;
}
template <typename T>
constexpr void operator--(vector<T> &v, int) noexcept {
  for (int i = 0; i < v.size(); i++) v[i]--;
}

random_device seed_gen;
mt19937_64 engine(seed_gen());

struct BiCoef {
  vector<mint> fact_, inv_, finv_;
  BiCoef(int n) noexcept : fact_(n, 1), inv_(n, 1), finv_(n, 1) {
    fact_.assign(n, 1), inv_.assign(n, 1), finv_.assign(n, 1);
    for (int i = 2; i < n; i++) {
      fact_[i] = fact_[i - 1] * i;
      inv_[i] = -inv_[MOD % i] * (MOD / i);
      finv_[i] = finv_[i - 1] * inv_[i];
    }
  }
  mint C(ll n, ll k) const noexcept {
    if (n < k || n < 0 || k < 0) return 0;
    return fact_[n] * finv_[k] * finv_[n - k];
  }
  mint P(ll n, ll k) const noexcept { return C(n, k) * fact_[k]; }
  mint H(ll n, ll k) const noexcept { return C(n + k - 1, k); }
  mint Ch1(ll n, ll k) const noexcept {
    if (n < 0 || k < 0) return 0;
    mint res = 0;
    for (int i = 0; i < n; i++)
      res += C(n, i) * mint(n - i).pow(k) * (i & 1 ? -1 : 1);
    return res;
  }
  mint fact(ll n) const noexcept {
    if (n < 0) return 0;
    return fact_[n];
  }
  mint inv(ll n) const noexcept {
    if (n < 0) return 0;
    return inv_[n];
  }
  mint finv(ll n) const noexcept {
    if (n < 0) return 0;
    return finv_[n];
  }
};

BiCoef bc(200010);

#pragma endregion

// -------------------------------

#pragma region FPS

// 引用：
// https://opt-cp.com/fps-implementation/

#define fastprod 1

#define drep2(i, m, n) for (int i = (m)-1; i >= (n); --i)
#define drep(i, n) drep2(i, n, 0)

template <class T>
struct FormalPowerSeries : vector<T> {
  using vector<T>::vector;
  using vector<T>::operator=;
  using F = FormalPowerSeries;

  F operator-() const {
    F res(*this);
    for (auto &e : res) e = -e;
    return res;
  }
  F &operator*=(const T &g) {
    for (auto &e : *this) e *= g;
    return *this;
  }
  F &operator/=(const T &g) {
    assert(g != T(0));
    *this *= g.inv();
    return *this;
  }
  F &operator+=(const F &g) {
    int n = (*this).size(), m = g.size();
    repi(i, min(n, m))(*this)[i] += g[i];
    return *this;
  }
  F &operator-=(const F &g) {
    int n = (*this).size(), m = g.size();
    repi(i, min(n, m))(*this)[i] -= g[i];
    return *this;
  }
  F &operator<<=(const int d) {
    int n = (*this).size();
    (*this).insert((*this).begin(), d, 0);
    (*this).resize(n);
    return *this;
  }
  F &operator>>=(const int d) {
    int n = (*this).size();
    (*this).erase((*this).begin(), (*this).begin() + min(n, d));
    (*this).resize(n);
    return *this;
  }
  F inv(int d = -1) const {
    int n = (*this).size();
    assert(n != 0 && (*this)[0] != 0);
    if (d == -1) d = n;
    assert(d > 0);
    F res{(*this)[0].inv()};
    while (res.size() < d) {
      int m = size(res);
      F f(begin(*this), begin(*this) + min(n, 2 * m));
      F r(res);
      f.resize(2 * m), internal::butterfly(f);
      r.resize(2 * m), internal::butterfly(r);
      repi(i, 2 * m) f[i] *= r[i];
      internal::butterfly_inv(f);
      f.erase(f.begin(), f.begin() + m);
      f.resize(2 * m), internal::butterfly(f);
      repi(i, 2 * m) f[i] *= r[i];
      internal::butterfly_inv(f);
      T iz = T(2 * m).inv();
      iz *= -iz;
      repi(i, m) f[i] *= iz;
      res.insert(res.end(), f.begin(), f.begin() + m);
    }
    return {res.begin(), res.begin() + d};
  }

// fast: FMT-friendly modulus only
#if fastprod
  F &operator*=(const F &g) {
    int n = (*this).size();
    *this = convolution(*this, g);
    (*this).resize(n);
    return *this;
  }
  F &operator/=(const F &g) {
    int n = (*this).size();
    *this = convolution(*this, g.inv(n));
    (*this).resize(n);
    return *this;
  }

#else
  F &operator*=(const F &g) {
    int n = (*this).size(), m = g.size();
    drep(i, n) {
      (*this)[i] *= g[0];
      REPI(j, 1, min(i + 1, m))(*this)[i] += (*this)[i - j] * g[j];
    }
    return *this;
  }
  F &operator/=(const F &g) {
    assert(g[0] != T(0));
    T ig0 = g[0].inv();
    int n = (*this).size(), m = g.size();
    repi(i, n) {
      REPI(j, 1, min(i + 1, m))(*this)[i] -= (*this)[i - j] * g[j];
      (*this)[i] *= ig0;
    }
    return *this;
  }

#endif

  // sparse
  F &operator*=(vector<pair<int, T>> g) {
    int n = (*this).size();
    auto [d, c] = g.front();
    if (d == 0)
      g.erase(g.begin());
    else
      c = 0;
    drep(i, n) {
      (*this)[i] *= c;
      for (auto &[j, b] : g) {
        if (j > i) break;
        (*this)[i] += (*this)[i - j] * b;
      }
    }
    return *this;
  }
  F &operator/=(vector<pair<int, T>> g) {
    int n = (*this).size();
    auto [d, c] = g.front();
    assert(d == 0 && c != T(0));
    T ic = c.inv();
    g.erase(g.begin());
    repi(i, n) {
      for (auto &[j, b] : g) {
        if (j > i) break;
        (*this)[i] -= (*this)[i - j] * b;
      }
      (*this)[i] *= ic;
    }
    return *this;
  }

  // multiply and divide (1 + cz^d)
  void multiply(const int d, const T c) {
    int n = (*this).size();
    if (c == T(1))
      drep(i, n - d)(*this)[i + d] += (*this)[i];
    else if (c == T(-1))
      drep(i, n - d)(*this)[i + d] -= (*this)[i];
    else
      drep(i, n - d)(*this)[i + d] += (*this)[i] * c;
  }
  void divide(const int d, const T c) {
    int n = (*this).size();
    if (c == T(1))
      repi(i, n - d)(*this)[i + d] -= (*this)[i];
    else if (c == T(-1))
      repi(i, n - d)(*this)[i + d] += (*this)[i];
    else
      repi(i, n - d)(*this)[i + d] -= (*this)[i] * c;
  }

  T eval(const T &a) const {
    T x(1), res(0);
    for (auto e : *this) res += e * x, x *= a;
    return res;
  }

  void differentiate() {
    int n = (*this).size();
    (*this) >>= 1;
    REPI(i, 1, n - 1)(*this)[i] *= (i + 1);
  }

  void integrate(bool ext = true) {
    if (ext) (*this).push_back(0);
    int n = (*this).size();
    (*this) <<= 1;
    REPI(i, 1, n)(*this)[i] *= bc.inv(i);
  }

  F operator*(const T &g) const { return F(*this) *= g; }
  F operator/(const T &g) const { return F(*this) /= g; }
  F operator+(const F &g) const { return F(*this) += g; }
  F operator-(const F &g) const { return F(*this) -= g; }
  F operator<<(const int d) const { return F(*this) <<= d; }
  F operator>>(const int d) const { return F(*this) >>= d; }
  F operator*(const F &g) const { return F(*this) *= g; }
  F operator/(const F &g) const { return F(*this) /= g; }
  F operator*(vector<pair<int, T>> g) const { return F(*this) *= g; }
  F operator/(vector<pair<int, T>> g) const { return F(*this) /= g; }
};

using fps = FormalPowerSeries<mint>;
using sfps = vector<pair<int, mint>>;

void add_ext(fps &f, fps &g) {
  f.resize(max(f.size(), g.size()));
  f += g;
}

void prod_ext(fps &f, fps &g) {
  f.resize(f.size() + g.size() - 1, 0);
  f *= g;
}

void prod_ext(fps &f, sfps &g) {
  int m = 0;
  for (auto [d, c] : g) {
    if (m < d) m = d;
  }
  f.resize(f.size() + m);
  f *= g;
}

#pragma endregion

void solve() {
  int n, k;
  cin >> n >> k;
  vector<int> a(n);
  cin >> a;
  vector<fps> L(n + 1), R(n + 1);
  fps e(k + 1, 0);
  e[0] = 1;
  L[0] = R[n] = e;
  rep(i, n) {
    L[i + 1] = L[i];
    L[i + 1].multiply(a[i], 1);
  }
  for (int i = n; i > 0; i--) {
    R[i - 1] = R[i];
    R[i - 1].multiply(a[i - 1], 1);
  }
  if (L[n][k].val() == 0) {
    cout << -1 << "\n";
    return;
  }
  int cnt = 0;
  rep(i, n) {
    fps f = L[i] * R[i + 1];
    if (f[k].val() == 0) cnt++;
  }
  cout << cnt << "\n";
}

int main() { solve(); }