#include<bits/stdc++.h>
#define ll long long
using namespace std;
int n,l,a[200],mid;
int ans;
int main(){
	freopen("device.in","r",stdin);
	freopen("device.out","w",stdout);
cin>>n>>l;
for(int q=1;q<=n;q++) cin>>a[q];
sort(a+1,a+n+1);
//mid=a[n/2+1];
//cout<<mid;

//中点在点上 
for(int q=2;q<n;q++)
{
	int c=a[q],flag=1;
	int x,y;
	x=y=q;
	while(x>0&&y<=n)
	{
		
		if(c-a[x]!=a[y]-c) flag=0;
		x--,y++;
	}
	if(flag==1) ans++;
}
//中点在两点间 
for(int q=1;q<n;q++)
{
	double c=a[q]+a[q+1];
	c/=2;
//	cout<<c<<endl;
	int flag=1;
	int x=q,y=q+1;
	while(x>0&&y<=n)
	{
		if(double(c-a[x])!=double(a[y]-c)) flag=0;
		x--,y++;
	}
	if(flag==1) ans++;
}
cout<<ans;
return 0;
}