#include <bits/stdc++.h> using namespace std; int n; int cnt; int x; bool check(long long n){ long long r = 0; long long a; a = n; while (n != 0){ int g = n % 10; n /= 10; r *= 10; r += g; } return r == a; } bool pdss(int x) { if (x < 2) { return 0; } bool flag = 1; for (int i = 2; i <= sqrt(x); i++) { if (x % i == 0) { flag = 0; break; } } return flag; } int main() { scanf("%d",&n); for (int i = 11; i <= n; i++) { if (pdss(i) == 1) { if (check(i) == true) { cnt++; } } } cout << cnt; return 0; }