#include <stdio.h>
#include <math.h>
#define dim 2000001
long i, j, n, s=0;
bool c[dim];

void ciur(long n)
	{
   c[2]=1;
   for (i=3;i<=n;i+=2)
   	c[i]=1;
   for (i=3;i<=sqrt(n);i+=2)
   	for (j=i;j<=n/i;j++)
      	c[i*j]=0;
   }
int main(void)
{
freopen("ciur.in", "r", stdin);
freopen("ciur.out", "w", stdout);
scanf("%ld", &n);
ciur(n);
for (i=2;i<=n;i++)
	if (c[i]==1)
   	s++;
printf("%ld", s);
fcloseall();
return 0;
}