#include<stdio.h>
char v[2000005];
long int i,j,n,k;
int main()
{FILE *fin,*fout;
fin=fopen("ciur.in","r");
fout=fopen("ciur.out","w");
fscanf(fin,"%ld",&n);
for(i=2;i<=n;i++)
  v[i]=1;
for(i=2;i<=n;i++)
  if(v[i]==1)
    {k++;
     for(j=i+i;j<=n;j=j+i)
        v[j]=0;
    }
fprintf(fout,"%ld",k);
fclose(fin);
fclose(fout);
return 0;
}