#include<bits/stdc++.h>
using namespace std;
int n,len;
int num[110];
map<int,int> xb;
bool check(int i)
{
    if(i<=n/2)
    {
        for(int j=1;j<i;j++)
            if(xb[num[i]+(num[i]-num[j])]==0)
                return false;
        return true;
    }
    else
    {
        for(int j=i+1;j<=n;j++)
            if(xb[num[i]-(num[j]-num[i])]==0)
                return false;
        return true;
    }
}
int main()
{
    freopen("device.in","r",stdin);
    freopen("device.out","w",stdout);
    int ans=0,a;
    cin>>n>>len;
    for(int i=1;i<=n;i++)
    {
        cin>>a;
        xb[a]=1;
        num[i]=a;
    }
    sort(num+1,num+1+n);
    for(int i=1;i<=n;i++)
        if(check(i))
            ans++;
    cout<<ans<<endl;
}