#include<fstream>

using namespace std;

ifstream cin("ciur.in");
ofstream cout("ciur.out");

int i,j,k,n;

bool ciur[2000005];

int main()
{
	cin>>n;
	int nmax=2000005;
	for(i=2;i<=nmax;++i){
		if(!ciur[i]) for(j=2;i*j<nmax;++j)ciur[i*j]=1;
	}
	for(i=2;i<=n;++i) 
		if(!ciur[i])++k;
	cout<<k;
	
	return 0;
}