#include <fstream>
#include <iostream>
#include <cmath>

using namespace std;

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

class Eratosthenes{
	int n; 
	int *lowerPrimes; // un vector ce va tine numarul de nr prime mai mici decat n
	int *sieve; // will basically act as a bitmap, a nr will be prime if its corresponding bit is 0
	int bits[35]; // bit i will be 2 to the power of i
	inline void set(int x){
		int posInt=x/32;
		int posBit=x%32;
		sieve[posInt]|=bits[posBit];
	}
	inline bool isSet(int x){
		int posInt=x/32;
		int posBit=x%32;
		return sieve[posInt]&bits[posBit];
	}
public:
	Eratosthenes(int);
	void createLowerPrimes();
	int countPrimes(int);
};

Eratosthenes::Eratosthenes(int value){
	int i,j;
	n=value;
	sieve=new int[(n>>5)+1];
	for(i=0;i<=(n>>5);++i)
		sieve[i]=0;
	bits[0]=1;
	for(i=1;i<32;++i)
		bits[i]=bits[i-1]<<1;
	for(i=4;i<=n;i+=2)
		set(i);
	for(i=3;i*i<=n;i+=2){
		if(!isSet(i)){
			for(j=i*i;j<=n;j+=i){
				set(j);
			}
			continue;
		}
	}
}

void Eratosthenes::createLowerPrimes(){
	int i;
	lowerPrimes=new int[n+1];
	lowerPrimes[0]=lowerPrimes[1]=0;
	for(i=1;i<=n;++i){
		if(!isSet(i)){
			lowerPrimes[i]=lowerPrimes[i-1]+1;
			continue;
		}
		lowerPrimes[i]=lowerPrimes[i-1];
	}
}
int Eratosthenes::countPrimes(int value){
	int counter=0;
	for(int i=2;i<=n;++i){
		if(!isSet(i)){
			counter++;
		}
	}
	return counter;
}
int main(){
	int n;
	in>>n;
	Eratosthenes ciur(n);
	out<<ciur.countPrimes(n);
	return 0;
}