#include<cstdio>
#include<bitset>
using namespace std;
bitset<2000005> a;
int main () {
	int i,j,n,k;
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%d",&n);
	for(i=2;i*i<=n;++i)
		if(a[i]==0)++k;
			for(j=i*i;j<=n;j+=i)
				a[j]=1;
	printf("%d",k);
return 0;
}