#include <iostream>
using namespace std;

#define MAX 1000000
int prime[MAX];

int main()
{
	int number,count=0;
	prime[0] = prime[1] = 0;

	for(int i=2;i<MAX;i++)
	{
		prime[i] = 1;
	}
	for(int i=2;i<1001;i++)
	{
		if(prime[i])
		{
			for(int j=2*i;j<MAX;j += i)
			{
				prime[j] = 0;
			}
		}
	}

	while(cin >> number)
	{
		count = 0;
		for(int i=2;i<=number;i++)
		{
			count += prime[i];
		}
		printf("%d\n",count);
	}

	return 0;
}