#include<cstdio>
#define l 2000005
using namespace std;

short a[l]={0};
long n;
int nr=0;

void citeste()
{
	freopen("ciur.in","r",stdin);
	
	scanf("%ld",&n);
	
	fclose(stdin);
}

void ciur()
{
	for(int i=2;i<=n;i++)
	{
		if(!a[i]) 
		{
			for(int j=2;j*i<=n;j++) a[i*j]=1;
            nr++;
		}
	}	
}



void afiseaza()
{
	freopen("ciur.out","w",stdout);
	
    printf("%d\n",nr);
	
	fclose(stdout);
}

int main()
{
	citeste();
	ciur();
	afiseaza();
	
	return 0;
}