#include<stdio.h>
#define N 2000001
char v[N];
int s=0,n,i,j;
void ciur()
	{
		for(i=2;i<=n;i++)
		{if(!v[i])
			for(j=i+i;j<=n;j+=i)
			v[j]=1;
		}
		
}

int main()
	{
		freopen("ciur.in","r",stdin);
		freopen("ciur.out","w",stdout);
		scanf("%d",&n);
		ciur();
	for(i=2;i<=n;i++)
			if(!v[i])s++;
printf("%d\n",s);
}