#include <iostream>
using namespace std;

int a[30002];
int b[30002];

int main()
{
	int n;
	cin>>n;
	int i,j;
	int change;
	for(i=0;i<n;i++)
		cin>>a[i];
	b[0] = a[0];
	j=0;
	if(b[0]==1)change = -1;
	else change=0;
	for(i=1;i<n;i++)
	{
		if(a[i]==2)
		{
			b[++j]=a[i];
			if(change==-1)
				change = j;
		}
		else if(a[i]==1&&change==-1)b[++j]=a[i];
		else 
		{
			b[change]=a[i];
			change++;
			if(change>j)
				change = -1;
		}
	}
	cout<<n-j-1<<endl;
}