#include <fstream.h>
ifstream fin("ciur.in");
ofstream fout("ciur.out");
char a[2000001];
long i=1,n,j,nr;
int main() {
	fin>>n;
	for(i=1;i<=n;++i)
		a[i]=1; //atribuim fiecarui element din vector valoarea 1
	for(i=2;i<=n;++i)
		if(a[i]==1)	{
			nr++;
			for(j=2*i;j<=n;j+=i)
				a[j]=0;
		}
	fout<<nr;
	fin.close();
	fout.close();
	return 0;	
}