#include<stdio.h>
bool v[2000001];
int n;

int main(){
  freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%d",&n);
	v[1]=1;
	int nr=0;
	for(int i=2;i<=n;i++)
		if(!v[i]){
			nr++;
			for(int j=i;j<=n;j+=i)
				v[j]=1;
		}
		printf("%d",nr);
	return 0;
}