#include <cstdio>
using namespace std;
bool prime[2000005];
int N;

int main(){

	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);

	scanf("%d\n",&N);

	int nr=0;

	for (int i=1;i<=N;++i) prime[i]=true;

	for (int i=2;i<=N;++i)
		if (prime[i]){
			++nr;
			for (int j=i+i;j<=N;j+=i) prime[j]=false;
		}

	printf("%d\n",nr);

	fclose(stdout);
	fclose(stdin);

	return 0;
}