#include<stdio.h>

int n,i,j,kkt,k;

char a[2000000];

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

	scanf("%d",&n);

	for(i=2; i<=n; ++i)
	{
		if(a[i]==0)
		{
			++kkt;

			k=2;

			j=i*k;

			while(j<=n)
			{
				a[j]=1;

				++k;

				j=i*k;
			}
		}
	}
	printf("%d",kkt);

	return 0;
}