#include <cstdio>
#define Maxn 2000001
using namespace std;
FILE *f1, *f2;
int n,prime,i,j;
short int nr[Maxn];
int main()
{
	f1 = freopen("ciur.in", "r", stdin);
	scanf("%i", &n);
	fclose(f1);
	nr[0]=nr[1]=0;
	for(i=2;i<=n;i++) nr[i] = 1;
	for(i=2;i<=n;i++)
	{
		if(nr[i])
		{
			prime ++;			
			for(j=i+i;j<=n;j+=i) nr[j] = 0;
		}
	}
	f2 = freopen("ciur.out", "w", stdout);
	printf("%i\n", prime);
	
	fclose(f2);
	return 0;
}