1 # include <stdio.h>
 2 
 3 int search(int a[], int n, int v)    //這個好像是效率最高的
 4 {
 5     int left = -1, right = n, middle;
 6     while(left+1 != right)
 7     {
 8         middle = left + (right-left) / 2;
 9         if(a[middle] < v)
10             left = middle;
11         else
12             right = middle;
 
13     }
14     if(right >= n || a[right] != v)
15         right = -1;
16     return right;
17 }
18 
19 int search1(int a[], int n, int v)
20 {
21     int left = 0, right = n-1, middle;
22     while(left <= right)
23     {
24         middle = (left+right) / 2;
25         if(a[middle] > v)
26         right = middle - 1
 
;
27         else if(a[middle] < v)
28         left = middle +1;
29         else
30         return middle;
31     }
32     return -1;
33 }
34 
35 int search2(int a[], int n, int v)
36 {
37     int left = 0, right = n, middle;
38     while(left < right)
39     {
40         middle = (right + left) / 2
 
;
41         if(a[middle] > v)
42         right = middle;
43         else if(a[middle] < v)
44         left = middle + 1;
45         else
46         return middle;
47     }
48     return -1;
49 }
50 
51 int a[1000000];
52 int main(void)
53 {
54     int n, i, t, ans;
55     while(~scanf("%d", &n))
56     {
57         for(i = 0; i < n; i++)
58             scanf("%d", &a[i]);
59         scanf("%d", &t);
60         ans = search(a, n, t);
61         if(ans <= 0)
62             printf("NO\n");
63         else
64             printf("YES\n");
65     }
66 
67     return 0;
68 }