#include<stdio.h>
int main()
{FILE *f=fopen("ciur.in","r");
 FILE *g=fopen("ciur.out","w");
 int n,i;
 int b[1500];

 fscanf(f,"%d",n);
 fclose(f);
 int max=1,j;
 b[0]=2;
 int ok;
 for(i=3;i<n+1;i++)
   {ok=0;
    for(j=0;j<max;j++)
        if(i%b[j]==0)
          ok=1;
    if(ok==0)
      b[max++]=i;
   }
 fprintf(g,"%d",max);
 fclose(f);
 return 0;
}