#include <stdio.h>
#include <fstream>
using namespace std;
#define mx 2000005

bool a[mx];
int main()
{
	ofstream out("ciur.out");
	ifstream in("ciur.in");
	long long c=0,i,j;
	//FILE *in=fopen("ciur.in","r"),*out=fopen("ciur.out","w");
	long long n;
	//fscanf(in,"%d",&n);
	in>>n;
	for(i=2;i<=n/2+1;i++)
	{
		if(a[i]==0)
		{
			c++;
			for(j=i+i;j<=n;j+=i)
			{
				a[j]=1;
			}
		}
	}
	//fprintf(out,"%i",c);
	out<<c;
}