#include <stdio.h>
int main()
{
    int low, high, i, flag,c=0,s;
    while(scanf("%d",&high)==!EOF)
       {
           int start = 2;

            while (start <= high)
            {
                flag = 0;
                s = sqrt(start);


                    for(i = 2; i <= start/2; i++)
                    {

                        if(start % i == 0)
                        {
                            flag = 1;
                            break;
                        }
                    }

                    if (flag == 0)
                    {
                          c++;

                    }
                    start++;

            }
                printf("%d\n",c); c=0;



       }
    return 0;
}