#include<cstdio>
#include<set>

using namespace std;


unsigned long N;
unsigned long T;
int s[2000010];
int main(){
	unsigned long i,j;
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	
	scanf("%ld",&N);
	for(i=2;i<=N;i++){
		if(s[i]==0){
			++T;
			for(j=2;j<=N+2/j;j++){
				s[i*j]=1;
			}
		}
	}

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