#include<cstdio>
#include <cmath> 
using namespace std;
bool a[2000005]; 
int main () {
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	int i,j,n,k=1;
	scanf("%d",&n);
	for(i=3;i*i<=n;i+=2)
		if(!a[i]){++k;
			for(j=i+i;j<=n;j+=i)
				a[j]=1;
		}
	printf("%d",k);
	return 0;
}