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