#include <bits/stdc++.h>
using namespace std;
int main(){
	int n, num[10007], lei[10007] = {0}, sum = 2;
	cin >> n;
	for(int i = 1; i <= n; i++){
		cin >> num[i];
	}
	if(n == 1 && num[1] == 1){
		cout << 1 << endl;
		return 0;
	}
	lei[1] = 1;
	for(int i = 2; i <= n + 1; i++){
		lei[i] = num[i - 1] - lei[i - 1] - lei[i - 2];
		if(lei[i] != 1 && lei[i] != 0){
			sum--;
			break;
		}
	}
	if(lei[n + 1] != 0){
		sum--;
	}
	lei[1] = 0;
	for(int i = 2; i <= n + 1; i++){
		lei[i] = num[i - 1] - lei[i - 1] - lei[i - 2];
		if(lei[i] != 1 && lei[i] != 0){
			sum--;
			break;
		}
	}
	if(num[n + 1] != 0){
		sum--;
	}
	cout << sum << endl;
	return 0;
}