#include <cstdio>
#include <bitset>
#include <cmath>
using namespace std;
bitset<2000001>v;
int n,i,j,nr=1,sqrtn;
int main()
{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%d",&n);
	sqrtn=sqrt((double)n)+1;
	for (i=3;i<=sqrtn;i+=2)
		if (!v[i])
			for (j=i*i;j<=n;j+=i)
				v[j]=1;
	for (i=3;i<=n;i+=2)
		if (!v[i])
			nr++;
	printf("%d\n",nr);
	fclose(stdin);
	fclose(stdout);
}