1 #include <bits/stdc++.h>
2 using namespace std;
3 typedef long long ll;
4 typedef double db;
5 #define INF 0x3f3f3f3f
6 #define _for(i,a,b) for(int i = (a);i < b;i ++)
7 #define _rep(i,a,b) for(int i = (a);i > b;i --)
8 #define mod 20100403
9
10 inline ll read()
11 {
12 ll ans = 0;
13 char ch = getchar(), last = ' ';
14 while(!isdigit(ch)) last = ch, ch = getchar();
15 while(isdigit(ch)) ans = (ans << 1) + (ans << 3) + ch - '0', ch = getchar();
16 if(last == '-') ans = -ans;
17 return ans;
18 }
19 inline void write(ll x)
20 {
21 if(x < 0) x = -x, putchar('-');
22 if(x >= 10) write(x / 10);
23 putchar(x % 10 + '0');
24 }
25 int n;
26 int ans = 2;
27 int a[10003];
28 int b[10003];
29 void check()
30 {
31 _for(i,2,n+2)
32 {
33 b[i] = a[i-1]-b[i-1]-b[i-2];
34 if(b[i]!=1&&b[i])
35 { ans --;break;}
36 if(i==n+1&&b[i])
37 { ans --;break;}
38 }
39 }
40 int main()
41 {
42 n = read();
43 b[0] = 0;
44 _for(i,1,n+1)
45 a[i] = read();
46
47 b[1] = 1;
48 check();
49 b[1] = 0;
50 check();
51 write(ans);
52 return 0;
53 }
