#include <cstdio>
#include <bitset>
using namespace std;
bitset <2000003> prime;
int n;
void ciur ()
{
	prime[0]=1;prime[1]=1;
	for(int i=2;i<=n;++i)
		if(prime[i]==0)
			for(int j=2;i*j<=n;++j)\
				prime[i*j]=1;
}
int cnt ()
{
	int kontor=0;
	for(int i=2;i<=n;++i)
		if(prime[i]==0)
			kontor++;
	return kontor;
}
int main ()
{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%d", &n);
	ciur();
	printf("%d", cnt());
	return 0;
}