#include<stdio.h>
FILE *f,*g;
char prim[2000005];

int main()
 { unsigned long int n,i,j;
 long nr=0;

      f=fopen("ciur.in","r");
      g=fopen("ciur.out","w");
    fscanf(f,"%ld",&n);

      for(i=2;i<=n;i++)
         prim[i]=1;
      for (i=2;i<=n;i++)
          if(prim[i])
             {nr++;
               for (j=i+i;j<=n;j+=i)
                  prim[j]=0;
             }
        fprintf(g,"%ld",nr);
        fclose(f);
        fclose(g);

   return 0;

     }