#include <cstdio>
#define MAX 2000001
char ciur[MAX];
int cnt,n,j,i;
int main()
{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%d",&n);
	for (i = 2; i <= n; ++i)
		ciur[i] = 1;
	for (i = 2; i <= n; ++i)
		if(ciur[i])
		{
			++cnt;
			for (j = i+i; j <= n; j += i)
				ciur[j] = 0;
		}
	printf("%d ",cnt);
	return 0;
}