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

int count_prime_number(int n){
	if(n < 2){
		return 0;
	}
	if(n == 2){
		return 1;
	}
	int count = 1;	//2??????
	for(int i = 3; i <= n; i += 2){
		int k = 0;
		for(int j = 3; j <= sqrt(i); j += 2){
			if(i % j == 0){
				k=1;
				break;
			}
		}
		if(k==0){
			count++;
		}
	}
	return count;
}

int main(){
	vector<int> results;
	int in_num;
	while(cin >> in_num){
		results.push_back(count_prime_number(in_num));
	}
	for(auto result : results){
		cout << result << endl;
	}
	return 0;
}