#include<stdio.h>
char a[2000000];
long int i,j,n,cont,d,k;
int main()
{FILE *f,*g;
f=fopen("ciur.in","r");
g=fopen("ciur.out","w");
      fscanf(f,"%ld",&n);
   for(i=2;i<=n;i++)a[i]=1;
   for(i=2;i<=n;i++)
  if(a[i]==1)
    {cont++;
    for(j=i+i;j<=n;j+=i)
        a[j]=0;
        
        }
               
fprintf(g,"%ld",cont);
fclose(f);
fclose(g); 
return 0;
}