#include<fstream>
#define endl "\n";

using namespace std;

	int main(){
			ifstream fin("ciur.in");
			ofstream fout("ciur.out");
		char v[2000001]={0};
		int i,j,n,k=0;
		
			fin>>n;
			
				  for(i=2;i*i<=n;i++)
						  if(!v[i])
								  for(j=2;j*i<=n;j++)
										  v[j*i]=1;
							k=0;
							for(i=2;i<=n;i++)
									if(!v[i]) k++;
							fout<<k;
	return 0;
	}