#include <stdio.h>
char v[2000000];
int main ()
{ int n,i,j,nr=0;
FILE *f=fopen("ciur.in","r");
FILE *g=fopen("ciur.out","w");
fscanf (f,"%d",&n);
for (i=2; i<=n; i++)
	if (v[i]==0)
                   {
                      nr++;
                       for (j=2*i; j<=n; j+=i)   v[j]=1;
	}
fprintf(g,"%d",nr);
fclose (f);
fclose (g);
return 0;
}