
#include <bits/stdc++.h>
using namespace std;

void Sieve(int n)
{
	bool prime[n+1];
	int c=0;
	memset(prime, true, sizeof(prime));

	for (int p=2; p<=n; p++)
	{
		if (prime[p] == true)
		{
			for (int i=p*2; i<=n; i += p)
				prime[i] = false;
		}
	}
	for (int p=2; p<=n; p++)
	if (prime[p])
		c++;
		cout<<c<<endl;
}

int main()
{
	int n;
	while(cin>>n){
        Sieve(n);
	}

	return 0;
}