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