#include<iostream>
#include<vector>
using namespace std;

int main()
{
	long int n,m;
	while(cin>>n){
		vector<int> number(1000000,0);
		int ans=0;

		for(int i=2;i<=n;i++){
			if(number[i]==0){
				ans++;
				//cout<<i<<endl;
				for(m=i;m<=n;m+=i){
					number[m]=1;
				}
			}
		}
		cout<<ans<<endl;
	}
}