#include <fstream.h>
#include <string.h>
long n,i,j,k,np,ok;
char v[20000001];
ifstream fin ("ciur.in");
ofstream fout ("ciur.out");
int main()
{
	fin>>n;
	np=n-1;
	for(i=2;i<=n+1;i++)
		v[i]=1;
	for(i=2;i<=n;i++)
	{
		ok=1;
		for(j=2;j*j<=i;j++)
			if(i%j==0)
				ok=0;
			if(ok)
				for(k=2;k*i<=n;k++)
					if(v[k*i]=='1')
					{
						v[k*i]='0';
						np--;
					}
	}
	fout<<np;
	return 0;
}