# include <stdio.h>
# include <math.h>
int main()
{
	int n,a[100];
	int i,j,k,count,max=2,z;
	scanf("%d",&n);
	for(i=0;i<n;i++)
	scanf("%d",&a[i]);
	for(i=0;i<n;i++)
	for(j=i+1;j<n;j++)
	if(fabs(a[i]-a[j])<=1)
	{
		for(k=j+1,z=j,count=2;k<n;k++)
		if(a[i]!=a[z])
		{
			if((fabs(a[i]-a[k])<=1)&&(fabs(a[z]-a[k])<=1))
		count++;
		}
		else
		{
			if((fabs(a[i]-a[k])<=1))
			{
				if(a[i]!=a[k])
				z=k;
				count++;
			}
		}
		if(max<count)
		max=count;
	}
	printf("%d\n",max);
	return 0;
}