#include <iostream>
#include <cmath>
#include <cstdio>
#include <time.h>     // for clock()
using namespace std;

/*
1???2 ?????? n ?????§?????´??°???????????????
2??????????????£???????????°????????§???????°?????????????????????? p ??¨?????????????????????????????????????????°?????? p ??¨?????????
p ??\?????? p ????????°?????¨????¶????????????????
3???2??????????????°?????????????????????p ??? ???n ????¶??????????????????????????????????????????£?????????????´???°???
*/
// ??¨????????????????????????
int SieveOfEratosthenes(int num) {
	
	if (num < 2) {
		return 0;
	}
	// num???????´???°?????°
	int count = 0;
	bool fl[1000001];
	memset(fl, true, sizeof(fl));
	for (int i = 2; i <= sqrt(num); i++) {
		if (fl[i]) {
			for (int j = 2; j*i <= num; j++) {
				fl[i*j] = false;
			}
		}
	}
	for (int i = 2; i <= num; i++) {
		if (fl[i]) {
			count++;
		}
	}
	return count;
}

int main() {

	int num = 0;
	while (cin >> num) {
		//clock_t start = clock();    // ??????????????????
		cout << SieveOfEratosthenes(num) << endl;
		//clock_t end = clock();     // ????????????
		//std::cout << "duration = " << (double)(end - start) / CLOCKS_PER_SEC << "sec.\n";
	}
	return 0;
}