#include<stdio.h>
int n;
char v[2097152];
int main()
{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%d",&n);
	long long i,j,nr=0;
	for(i=2;i<=n;i++)
		if(v[i]==0)
		{
			nr++;
			for(j=i*i;j<=n;j=j+i)
				v[j]=1;
		}
	printf("%lld\n",nr);
	return 0;
}