#include<iostream>
using namespace std;
int arr[100000001] = { 0 };
int main()
{
	int n, num = 0;
	cin >> n;
	for (int i = 2; i <= n; i++)
	{
		if (!(arr[i]))
		{
			for (int j = i * 2; j <= n; j += i)
				arr[j] = 1;
			num++;
		}
	}
	cout << num;
	return 0;
}