#include<bits/stdc++.h>
using namespace std;
bool IsPrime(int n){
	for(int i=2;i*i<=n;i++)if(n%i==0)return false;
	return true;
}
signed main(){
	int n,ans=0;
	cin>>n;
	for(int i=2;i<=n;i++)if(IsPrime(i))ans++;
	cout<<ans;
}