#include<stdio.h>
bool v[2000005];
int main()
{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	int n,i,j,m;
	scanf("%d",&n);
	m=0;
	for(i=2;i<=n;i++)
		if(v[i]==0)
		{
			for(j=i+i;j<=n;j=j+i)
				v[j]=1;
			m++;
		}
			printf("%d",m);
			return 0;
}