#include <cstdio>
int j,m,n,i;
bool marcat[2000000];
int p[1000000];
int main ()
{
	m=0;
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
		scanf("%d",&n);
		for (i=2;i*i<n;i++)
			if (!marcat[i])
				for (j=i*i;j<=n;j=j+i)
					marcat[j]=true;
				for (i=2;i<=n;i++)
					if (!marcat[i])
					{
						m=m+1;
						p[m]=i;
					}
	printf("%d",m);
	return 0;
}