#include<cstdio>

char a[2000001];

void ciur(int &n)
{
	scanf("%d",&n);
	int i,j;
	for(i=2; i<=n; ++i)
		a[i]=1;
	
	int k=0;
	
	for(i=2; i<=n; ++i)
	{
		if(a[i]==1)
		{
			k++;
			for(j=2*i;j<=n; j+=i)
				a[j]=0;
		}
	}
	
	printf("%d",k);
}


int main()
{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	
	int n;
	ciur(n);
	
	return 0;
}