#include<iostream>
#include<fstream>

using namespace std;
int a[2000000002];

int main()
{
	int n,i,j,contor=0;
	
	ifstream fin("ciur.in");
	fin>>n;
	fin.close();
	
	for(i=2;i<=n;i++)
		if(a[i]== 0 )
		{
			for(j=2;j<=n;j++)
				a[i*j]=1;
		}
	for(i=1;i<n;i++)
		if(a[i]==0)
			contor++;
	ofstream fout("ciur.out");
	fout<<contor-1;
	fout.close();
	return 0;
}