#include<iostream>
#include<cmath>
#include<vector>
#include<string>
#include<stdlib.h>
using namespace std;
bool IsLeapNumber(int e)
{
	int t = sqrt(e);
	int i = 2;
	for (i; i <= t;i++) {
		if (e % i == 0)
			break;
	}
	if (i > t)
		return true;
	if (i <= t)
		return false;
}
int main()
{
	vector<int> vec;
	int N;
	cin >> N;
	int count = 0;
	for (int j = 2; j <= N; j++)
	{
		if (IsLeapNumber(j) == true)
			vec.push_back(j);
	}
	vector<int>::iterator it = vec.begin();
	for (it; it != vec.end()-1; it++)
	{
		if (*(it + 1) - *(it) == 2)
			count++;
	}
	cout << count;
}