#include<stdio.h>
long n,i,j,t;
char c[2000005];
void ciur()
{
	long i;
	for(i=2;i*i<=n;++i)
		if(!c[i])
			for(j=i+i;j<=n;j=j+i) c[j]=1;
	for(i=2;i<=n;++i) 
	{
		if(!c[i]) 
		{
			t++;
		}
	}
}
int main()
{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%ld",&n);
	ciur();
	printf("%ld\n",t);
	return 0;
}