#include<fstream>

using namespace std;
int main()
{
	ifstream f("ciur.in");
	ofstream g("ciur.out");
	long n,i,j,k=1;
	f>>n;
	bool v[n+1];
	for(i=2;i<=n;i++)v[i]=0;
	for(i=4;i<=n;i=i+2)v[i]=1;
	for(i=3;i<=n;i=i+2)if(v[i]==0){k++;for(j=3*i;j<=n;j=j+i)v[j]=1;}
	g<<k;
	f.close();
	g.close();
	return 0;
}