ans;
a[200000];
odd[200000],even[200000],oddc,evenc;
n,x,y;
c(int*a,int*b){return*a-*b;}
f(int x,int*a){
	int l=0,r=n;
	while(r-l>1){
		int m=(l+r)/2;
		if(a[m]>x)r=m;
		else l=m;
	}
	return l;
}
g(i){
	int l=abs(x-a[i]),r=x+a[i];
	//l以上r以下があればok
	int *aa;
	if(l%2==1){
		aa=odd;
	}else{
		aa=even;
	}
	int temp=f(l,aa);
	int temp2=f(r,aa);
	return l==aa[temp]||temp!=temp2;
}
main(){
	scanf("%d",&n);
	for(int i=0;i<n;i++){
		scanf("%d",a+i);
		if(a[i]%2==1)odd[oddc++]=a[i];
		else even[evenc++]=a[i];
	}
	qsort(a,n,4,c);
	qsort(odd,oddc,4,c);
	qsort(even,evenc,4,c);
	scanf("%d%d",&x,&y);
	x=abs(x)+abs(y);
	if(x==0){puts("0");return 0;}
	if(a[f(x,a)]==x){puts("1");return 0;}
	else{
		for(int i=0;i<n;i++)if(g(i)){puts("2");return 0;}
	}
	puts("-1");
}