#include <stdio.h>
 
int N, cnt;
 
int prim(int n)
{
   if(n==2)
      return 1;
   if(n<2 or n%2==0)
      return 0;
   for(int i=3;i*i<=n;i+=2)
      if(n%i==0)
          return 0;
   return 1;
}

 
int main(void)
{
    int i;
     
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
 
    scanf("%d", &N);
    for (i = 2; i <= N; ++i)
        if (prim(i))
            ++cnt;
    printf("%d\n", cnt);
 
    return 0;
}