#include<cstdio>

using namespace std;

void read();
void solve();

int n,v[2000000],x,i,j;

int main()
{
	read();
	solve();
}

void read()
{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%d",&n);
}

void solve()
{
	for(i=2;i<n;i++)
		if(v[i]==0)
		{
			x++;
			for(j=i+i;j<=n;j+=i)
				v[j]=1;
		}
	printf("%d",x);
}