#include<stdio.h>
int N,k,v[200001],j,i;

int main()
{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%d",&N);
	for( i = 2 ; i <= N ; ++i)
	{	if(v[i]==0)
			k++;
		for( j = i ; j <= N ; j += i)
			v[j]=1;
	}
	printf("%d",k);
	return 0;
}