using namespace std;
#include <stdio.h>
int n, c;
char a[2000001];
int main() 
{

	freopen("ciur.in", "r", stdin);
	freopen("ciur.out", "w", stdout);
	int i,j;
	scanf("%d",&n);
    for(i=2; i<=n; i++)
		  if (!a[i]) 
		{ ++c;
	    for (j = i+i; j<=n; j+=i)
				a[j]=1;
		}
    printf("%d\n", c);
    return 0;
}