#include <iostream>
using namespace std;
const int MAX = 1000000;

int main(){
	bool b[MAX] = {true};
	static int a[MAX] = {0,0};
	int n;
	for(int i = 2;i < MAX;i++){
		if(!b[i]){
			for(int j = 2;i*j < MAX;j++){
				b[i*j] = true;
			}
		}
		a[i] = a[i-1] + !b[i];
	}
	while(cin >> n){
		cout << a[n] << endl;
	}
	return 0;
}