#include <bits/stdc++.h>
using namespace std;
int a[10000005];
int sukablyat(int n) {
	memset(a, 1, sizeof(a));
	a[0] = a[1] = 0;
	int cnt = 0;
	for (int i = 1; i <= n; i ++) {
		if (a[i] == 0) {
			continue;
		}
		cnt ++;
		for (int j = 1; i * j <= n; j ++) {
			a[i * j] = 0;
		}
	}
	return cnt;
}
int k;
int main() {
	cin >> k;
	cout << sukablyat(k);
	return 0;
}