#include<iostream>
using namespace std;
int main(){
	long long int N,count[1000000];
		count[1] = 1;
		if(N<0)	break;
	for(int x=2;x<=1000000;x++){
		int flag = 0;
		for(int y=2;y<x;y++){
			if((x%y)==0)	flag = 1;
		}
		if(flag == 0)	count[i] = count[i-1]+1;
	}
	while(cin >> N){
		cout << count[N] << endl;
	}
	return 0;
}