/*
 * =====================================
 *
 * 	Task: Savey
 * 	User: fanzeyi
 * 	Lang: C
 * 	
 * =====================================
 */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>

int *lock;
int n;
int count=0;

void RemoveZero()
{
	int i;
	for(i=n-1;i>=0;i--)
	{
		if(lock[i]==1)
			break;
		n--;
	}
	return;
}

void digui(int num)
{
	if(num==n-1)
		return;
	int i;
	for(i=num;i<n;i++)
		if(lock[i]==1)
		{
			count-=1;
			digui(i+1);
			break;
		}
}

int main()
{
	FILE *fin=fopen("savey.in","r");
	FILE *fout=fopen("savey.out","w");
	fscanf(fin,"%d\n",&n);
	lock=(int*)malloc(sizeof(int)*n);
	int i;
	for(i=0;i<n;i++)
		fscanf(fin,"%d ",&lock[i]);
	RemoveZero();
	count+=pow(2,n)-1;
	digui(0);
	fprintf(fout,"%d",count+1);
	return 0;
}