#include <fstream>
#include <bitset>

using namespace std;

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

const int N=2000001;

bitset <N> biti;

int n,rez;

int main(){
	int i,j;
	in>>n;
	for(i=2;i*i<=n;++i){
		if(biti[i]==0){
			for(j=i*i;j<=n;j+=i)
				biti[j]=1;
		}
	}
	for(i=2;i<=n;i++){
		if(biti[i]==0){
			rez++;
		}
	}
	out<<rez;
	return 0;
}