#include <cstdio>

using namespace std;

FILE *f=fopen("ciur.in","r");
FILE *g=fopen("ciur.out","w");

int i,j,n,k;
bool v[999999];

int main()
{
    fscanf(f,"%d",&n);
    for(i=1;((i*i)<<1)+(i<<1)<=n;i++)
     if(v[i]==0)
      {
          for(j=((i*i)<<1)+(i<<1);(j<<1)+1<=n;j+=(i<<1)+1)
           v[j]=1;
      }
    for(i=1;2*i+1<=n;i++)
     if(v[i]==0) k++;
    fprintf(g,"%d",k+1);
    return 0;
}