using namespace std;
#include<fstream>
ifstream fin("ciur.in");
ofstream fout("ciur.out");
char v[2000005];
int main()
{
	int n,i,j,c=0;
	fin>>n;
	for(i=2;i<=n;i++)
		if(!v[i]) 
		{
			c++;
			for(j=i*i;j<=n;j=j+i)
				v[j]=1;
		}
	fout<<c;
	return 0;
}