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
9 inline ll read()
10 {
11 ll ans = 0;
12 char ch = getchar(), last = ' ';
13 while(!isdigit(ch)) last = ch, ch = getchar();
14 while(isdigit(ch)) ans = (ans << 1) + (ans << 3) + ch - '0', ch = getchar();
15 if(last == '-') ans = -ans;
16 return ans;
17 }
18 inline void write(ll x)
19 {
20 if(x < 0) x = -x, putchar('-');
21 if(x >= 10) write(x / 10);
22 putchar(x % 10 + '0');
23 }
24 int n;
25 int a[35];
26 int main()
27 {
28 n = read();
29 int cnt = 0;
30 bool rnt;
31 _for(i,1,n+1)
32 a[i] = read();
33 _for(i,1,n+1)
34 {
35 cnt ++;
36 if(!a[i])
37 {
38 if(cnt & 0x1)
39 rnt = false;
40 else
41 rnt = true;
42 break;
43 }
44 }
45 cnt = 0;
46 if(!rnt)
47 _rep(i,n,0)
48 {
49 cnt ++;
50 if(!a[i])
51 {
52 if(cnt & 0x1)
53 rnt = false;
54 else
55 rnt = true;
56 break;
57 }
58 }
59 if(rnt)
60 printf("YES\n");
61 else
62 printf("NO\n");
63 return 0;
64 }