#include <iostream>
#include <algorithm>
using namespace std;

void AOJ0009()
{
	int n = 0;
	int prime[100000];
	int count = 0;
	for (int i = 2; i <= 100000; i++)
	{
		int j = 2;
		bool flag = false;
		for (j = 2; j <= i; j++)
		{
			if (i % j == 0)
				break;
		}
		if (i == j)
		{
			prime[count] = i;
			count++;
		}
	}

	while (cin >> n)
	{
		count = 0;
		while (prime[count] <= n)
		{
			count++;
		}
		cout << count << endl;
	}
}
int main()
{
	//AOJ0005();
	//AOJ0007();
	AOJ0009();
	return 0;
}