#include<bits/stdc++.h>
#define mem(i,a) memset(i,a,sizeof(i))
#define inf 0x3f3f3f3f3f3f3f3f
#define PII pair<int,int>
#define int  long long
#define endl '\n'
using namespace std;
const int maxn = 3e5 + 5;
int a[maxn],b[maxn];
void solve() {
	int n,p;
	cin>>n>>p;
	for(int i=1;i<=n;i++){
		cin>>a[i];
		b[i]=a[i]%p;
		a[i]%=2;
	}
	if(p!=2){
		sort(b+1,b+n+1);
		if(b[1]!=b[n]){
			cout<<"-1"<<endl;
			return;
		}
		cout<<1<<endl;
		return;
	}
	
	int cnt=0;
	for(int i=3;i<=n;i++){
		if(i==1){
			if(a[i]!=a[n-1]){
				cout<<-1<<endl;
				return ;
			}
		}
		else if(i==2){
			if(a[i]!=a[n]){
				cout<<-1<<endl;
				return;
			}
		}
		else {
			if(a[i-2]!=a[i]){
				cout<<-1<<endl;
				return;
			}
		}
		cnt+=a[i];
	}
	if(cnt==n){
		cout<<1<<endl;
		return;
	}
	if(cnt==0){
		cout<<1<<endl;
		return;
	}
	cout<<2<<endl;
}
signed main() {
	cin.tie(0);
	cout.tie(0);
	ios::sync_with_stdio(0);
	// int _;
	// cin >> _;
	// while (_--)
		solve();
	return 0;
}