#include<fstream>
#include<iostream>
#include<vector>
#include<bitset>
using namespace std;

int main()
{
	int n,num=1;
	fstream fin("ciur.in", fstream::in);
	fstream fout("ciur.out", fstream::out);
	fin>>n;
	//cout<<n<<endl;
	//ector<char> v;
	//v.resize(n+1);
	bitset<2000000> bits;
	//v[4]=1;
	
	for(int j=4; j<n; j+=2)
		bits[j]=1;
	for(int i=3; i<n; i+=2)
	{
		//cout<<(char)(v[i]+48)<<" ";
		if(!bits[i])
		{
			for(int j=i*i; j<n; j+=i)
				bits[j]=1;
			num++;
		}
	}
	/*for(int i=2; i<n; ++i)
	{
		if(!bits[i])
			cout<<i<<" ";
	}*/
	
	fout<<num<<endl;
	//cout<<endl;
	
	
	fin.close();
	fout.close();
	return 0;
}