#include<stdio.h>
#include<math.h>
#define NMAX 2000001
bool c[NMAX];
int main()
{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	int n,i,j,lim,num=0;
	scanf("%d",&n);
	lim=(int)sqrt((double)n);
	c[0]=c[1]=1;
	for(i=4;i<=n;i+=2)
		c[i]=1;
	for(i=3;i<=lim;i+=2)
		if (c[i]==0)
			for(j=i*2;j<=n;j+=i)
				c[j]=1;
	for(i=2;i<=n;++i)
		if (c[i]==0)
			++num;
	printf("%d\n",num);
	return 0;
}