1 #include<cstdio>
 2 #include<cstring>
 3 using namespace std;
 4 int n,cnt=0;
 5 bool iss(int x)
 6 {
 7     for(int i=2;i*i<=x;i++)
 8         if(x%i==0)return false;
 9     return true;
10 }
11 bool ishws(int y)
12 {
13     char s[21];
14     sprintf(s,"%d",y);//sprintf()函数将数字转化为字符串 此处敲黑板，sprintf()很有用
15     int len=strlen(s);
16     for(int i=0,j=len-1;i<=len/2;i++,j--)
17         if(s[i]!=s[j])return false;
18     return true;
19 }
20 
21 int main()
22 {
23     scanf("%d",&n);
24     for(int i=11;i<=n;i++)
25     if(iss(i)&&ishws(i))cnt++;
26     printf("%d",cnt);
27 
28 }