#include<fstream>
#include<bitset>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
int n,x,nr=1;
bitset<2000001> v;
int main()
	{in>>n;
	for(int i=4;i<=n;i+=2)v.flip(i);
	for(int i=3;i<=n;i+=2)if(v[i]==0){nr++;
									for(int j=3*i;j<=n;j+=i)v.flip(j);
									}
	out<<nr<<'\n';
	out.close();
	return 0;
	}