#include<cstdio>
#include<set>

using namespace std;

unsigned long N;
unsigned long T;
int main(){
	set<unsigned long> s;
	unsigned long j;
	unsigned long i;

	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	
	scanf("%ld",&N);
	for(i=2;i<N;i++){
		if(s.find(i)==s.end()){
			++T;
			for(j=2;j<=N+2/j;j++){
				s.insert(i*j);
			}
		}
	}

	printf("%ld",T);
	
	return 0;
}