#include<stdio.h>
char v[2000005];
int n,i,k;
int main()
{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%d",&n);
	for(i=2;i<=n;i++)
	{
		if(!v[i])
		{
			k++;
			for(int j=2*i;j<=n;j+=i)
				v[j]=1;
		}
	}
	printf("%d",k);
	return 0;
}