#include<stdio.h>
#include<bitset>
using namespace std;
int n,rez=1;
bitset<1000000> c;
int main()
{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%d",&n);
	int i2;
	for(int i=3; i<=n; i+=2)
	{
		if(c[i>>1])
			continue;
		rez++;
		for(int j=i+(i2=i<<1); j<=n; j+=i2)
			c[j>>1]=1;
	}
	printf("%d\n",rez);
	return 0;
}