#include<stdio.h>
#include<math.h>
char ciur[2000010];
int nr;
int n;

int main()
{
     freopen("ciur.in","r",stdin);
     freopen("ciur.out","w",stdout);
     scanf("%d",&n);
     for(int i = 4; i <= n; i += 2)
      ciur[i] = 1;
     for(int i=2; i <= n; i++)
       if (!ciur[i])
      {
      for(int j = 2 * i ; j <= n; j+= i)
       ciur[j] = 1;
      nr++;
      }
     printf("%d",nr);
     return 0;
}