#include<stdio.h>
char v[2000010];
int i,j,n,k;

int main ()
{

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)
	{k++;
	 for (j=2*i;j<=n;j+=i)
	      v[j]=1;
	}

fprintf(g,"%d",k);
fclose(f);
fclose(g);
return 0;
}