#include<iostream.h>
#include<fstream.h>
ifstream f ("ciur.in");
ofstream g ("ciur.out");
int main()
{
	int n,nr,i,j;
	char prim[2000005];
    f >> n;
	f.close();
	cout<<"n="<<n;
	for (i=2; i<=n; i++)
		prim[i]=1;
	for (i=2; i<=n; i++)
		if (prim[i])
		{
			nr++;
			for (j=i+i; j<=n; j+=i)
				prim[j]=0;
		}
	g << nr;
	g.close();
	return 0;
}