#include <iostream>
#include <cmath>
using namespace std;
bool is_prime(int);
int reverse_num(int);
int main() {
	int n, count = 0;
	cin >> n;
	for (int i = 11; i <= n; i++) {
		if (is_prime(i)) {
			if (i == reverse_num(i)) {
				count++;
			}
		}
	}
	cout << count;
}
bool is_prime(int n) {
	if (n == 2 || n == 3) {
		return true;
	}
	for (int i = 2; i <= sqrt(n); i++) {
		if (n % i == 0) {
			return false;
		}
	}
	return true;
}
int reverse_num(int n) {
	int num;
	while (n > 0) {
		num = num * 10 + n % 10;
		n /= 10;
	}
	return num;
}