#include<iostream.h>
#include<fstream.h>

int main()
    {
    char v[2000001];long int k=0,i,j,n;
    fstream f("D:\\ciur.txt",ios::in),g("D:\\ciur.out",ios::out);
    f>>n;
    for(i=1;i<=n;i++)
                 v[i]='0';
    for(i=2;i<=n;i++)
               if(v[i]=='0')
                      {
                      k++;
                       for(j=i;j<=n;j+=i)
                               v[j]='1';
                       }
    g<<k;f.close();g.close();
    }