#include <iostream>
#include <fstream>

using namespace std;


int main()
{
    long n;
    FILE *f = fopen("ciur.in","r");
    fscanf(f,"%f", &n);
    int a[sizeof(n)];

    a[0] = 2;
    long k = 1,x = 3;
    while(x<=n)
    {
      int sw = 1;
      for(int i=0;i<k && sw;i++)
        if(x % a[i] == 0)
              sw = 0;

      if(sw)
        a[k++] = x;
      x += 2 ;
    }

    f = fopen("ciur.out","w");
    fprintf(f,"%f", k);

    return 0;
}