#include<stdio.h>
bool marcat[2000001];

int main()
{
	int n,i,j,nr=0;
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%d",&n);
	for(i=2;i*i<=n;i++)
		if(!marcat[i])
			for(j=i*i;j<=n;j+=i)
				marcat[j]=true;
	for(i=2;i<=n;i++)
		if(!marcat[i])
			nr++;
	printf("%d\n",nr);
	return 0;
}