//g++ 2.cpp -std=c++14 -O2 -I .
#include <bits/stdc++.h>
using namespace std;

#include <atcoder/all>
using namespace atcoder;

using ll = long long;
using ld = long double;

using vi = vector<int>;
using vvi = vector<vi>;
using vll = vector<ll>;
using vvll = vector<vll>;
using vld = vector<ld>;
using vvld = vector<vld>;
using vst = vector<string>;
using vvst = vector<vst>;

#define fi first
#define se second
#define pb push_back
#define eb emplace_back
#define pq_big(T) priority_queue<T,vector<T>,less<T>>
#define pq_small(T) priority_queue<T,vector<T>,greater<T>>
#define all(a) a.begin(),a.end()
#define rep(i,start,end) for(ll i=start;i<(ll)(end);i++)
#define per(i,start,end) for(ll i=start;i>=(ll)(end);i--)
#define uniq(a) sort(all(a));a.erase(unique(all(a)),a.end())

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

  int n,k;
  cin>>n>>k;

  if(k==0){
    cout<<0<<endl;
    return 0;
  }

  vi a(n);
  rep(i,0,n){
    cin>>a[i];
  }

  vvll prev(n+1);
  prev[0]={1};
  rep(i,0,n){
    vll x(k+1,0);
    x[0]++;
    x[a[i]]++;
    prev[i+1]=convolution(prev[i],x);
    while(prev[i+1].size()>1050){
      prev[i+1].pop_back();
    }
  }

  vvll afte(n);
  afte[0]={1};
  rep(i,0,n-1){
    vll x(k+1,0);
    x[0]++;
    x[a[n-1-i]]++;
    afte[i+1]=convolution(afte[i],x);
    while(afte[i+1].size()>1050){
      afte[i+1].pop_back();
    }
  }

  if(prev[n][k]==0){
    cout<<-1<<endl;
    return 0;
  }

  int ans=0;
  rep(i,0,n){
    vll l=prev[i];
    vll r=afte[n-1-i];
    vll gt=convolution(l,r);
    if(gt[k]==0){
      ans++;
    }
  }

  cout<<ans<<endl;
}