#include<iostream>
#include<cmath>
#include<cstring>
#include<string>
using namespace std;
int  n,m,j,k,s,x;
int  b[5800000];
bool a[100000000];
int main(){
	scanf("%d",&n);
	for (int i=2;i<=n;i++){
		if (a[i]==0){
		 	b[++s]=i;
		}
		for (int j=1;j<=s;j++){
			if (j*b[j]>n){
				break;
			}
				a[i*b[j]]=1;
				if (i%b[j]==0){
					break;
				}
		}
	}
	cout<<s;
	return 0;
}