#include<cstdio>
#include<bitset>

using namespace std;

const int Nmax = 2000000/2/8+1;

int N, rez;
bitset<Nmax> p;
 
//(p[i>>3]&(1<<(i&7))) == 0 if 2*i + 1 is prime
 
int eratostene(int n) {
	int i, j, nr = 1;
	for(i = 1; ((i * i) << 1) + (i << 1) <= n; i++) {      
		if(p[i] == 0) {
			for (j = ((i * i) << 1) + (i << 1); (j << 1) + 1 <= n; j += (i << 1) + 1) {
				p[i] = 1;
			}
		}
	}
	
	for(i = 1; 2 * i + 1 <= n; ++i)  
		if (p[i] == 0) 
			nr++;
  
	return nr;
}

int main() {
	
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	
	scanf("%d",&N);
	rez = eratostene(N);
	printf("%d\n",rez);
	
	return 0;
}