#include <stdio.h>
#include <stdlib.h>
#define File_in "ciur.in"
#define File_out "ciur.out"
int prim(int n){
  int i,j,ok;
  if(n==1||n==0)
    return 0;
  ok=1;
  for(i=2;i*i<=n;i++)
      if(n%i==0)
        ok=0;
    return ok;
}
int main()
{
    freopen(File_in, "r", stdin);
    freopen(File_out, "w", stdout);
    int n,i,nr=1;
    scanf("%d",&n);
    for ( i = 3; i <= n; i+=2)
    {
        if(prim(i))
            nr++;
    }
    printf("%d",nr);
    return 0;
}