#include<stdio.h>
FILE *f=fopen("ciur.in","r"),
     *g=fopen("ciur.out","w");
int k,pr[100000],i,n,j,ok;
int main()
{ fscanf(f,"%d",&n);
  pr[0]=2;
  pr[1]=3;
  pr[2]=5;
  k=2;
  i=7;
  while(i<n){ ok=1;
              for(j=1;j<=k&&ok;++j) if(i%pr[j]==0) ok=0;
              if(ok) pr[++k]=i;
              i+=2;
            }
  fprintf(g,"%d\n",k+1);
  fclose(f);
  fclose(g);
  return 0;
}