#include<stdio.h>
#define NMAX 2000001
FILE *fin,*fout;
int n,ciur[NMAX],nr=0;
void read()
{
    fin=fopen("ciur.in","r");
    fscanf(fin,"%d",&n);
    fclose(fin);
}
void solve()
{
    for(int i=2;i<=n;i++) ciur[i]=1;
    for(int i=2;i<=n;i++)
    {
        if(ciur[i])
            {   nr++;
                for(int j=2;j*i<=n;j++)
               ciur[j*i]=0;}
    }
}
void afisare()
{  //int nr=0;
    fout=fopen("ciur.out","w");

   fprintf(fout,"%d",nr);
   fclose(fout);
}
int main()
{
   read();
   solve();
   afisare();
   return 0;
}