#include<cstdio>
#include<bitset>

using namespace std;

#define Nmax 20000001

bitset <Nmax> viz;
int N, sol=1;

void eratostene() {
	int i, j;
	
	for(i=3; i<=N; i+=2) 
		if(!viz[i]) {
			sol++;
			for(j=i*2; j<=N; j+=i)
				viz[j]=1;
		}
}

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