#include <fstream>
#include <iostream>

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
	void set(int x){
		int posInt=x/32;
		int posBit=x%32;
		sieve[posInt]|=bits[posBit];
	}
	bool isSet(int x){
		int posInt=x/32;
		int posBit=x%32;
		return sieve[posInt]&bits[posBit];
	}
public:
	Eratosthenes(int value){
		int i,j;
		n=value;
		lowerPrimes=new int[n+1];
		lowerPrimes[0]=lowerPrimes[1]=0;
		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=2;i*i<=n;++i){
			if(!isSet(i)){
				lowerPrimes[i]=lowerPrimes[i-1]+1;
				for(j=i*i;j<=n;j+=i){
					set(j);
				}
				continue;
			}
			lowerPrimes[i]=lowerPrimes[i-1];
		}
		for(i=sqrt((float)n);i<=n;++i){
			if(!isSet(i)){
				lowerPrimes[i]=lowerPrimes[i-1]+1;
				continue;
			}
			lowerPrimes[i]=lowerPrimes[i-1];
		}
	}
	int countPrimes(int value){
		return lowerPrimes[value];
	}
};

int main(){
	int n;
	in>>n;
	Eratosthenes ciur(n);
	out<<ciur.countPrimes(n);
	return 0;
}