#include<fstream>
#include<math.h>
using namespace std;
int n, d, nrp, x, OK, rx, v[2000001], j;
int main(){
	ifstream cin("ciur.in");
	ofstream cout("ciur.out");
	cin>>n;
	for(x=2; x<=n; x++){
		if(v[x]==0){
			nrp++;
			for(j=x+x; j<=n; j+=x)
				v[j]=1;
		}
			
		 
	}

	cout<<nrp;
	return 0;
}