#include <fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int i,j,n,nr,f[2000010];
int main() {
	fin>>n;
	f[0]=1; f[1]=1;
	for (i=2;i<=n/2;i++) {
		for (j=2*i;j<=n;j+=i) {
			f[j]=1;
		}
	}
	for (i=1;i<=n;i++) {
		if (f[i]==0)
			nr++;
	}
	fout<<nr;
	return 0;
}