#include <stdio.h>
#include <math.h>

FILE *f,*g;

long p[2000000];

int main()
{

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

 long n,i,j,k=0;

 fscanf(f,"%ld",&n);


 i=2;
 while(i<=sqrt(n)){ if(p[i]==0){ for(j=i+i;j<=n;j=j+i) p[j]=1;
							i++;
			       }
			else i++;
		   }
 for(i=1;i<=n;i++) if(p[i]==1) k++;

 fprintf(g,"%ld" , k);

 fclose(f);
 fclose(g);

 return 0;

}