#include<stdio.h>
#include<math.h>
char ciur[2000002];
int nr;
int n;

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