#include<stdio.h>
#pragma warning(disable:4996)
using namespace std;

int main() {
	freopen("ciur.in", "r", stdin);
	freopen("ciur.out", "w", stdout);

	int n, count = 0, *a;
	a = new int[2000000];

	scanf("%d", &n);

	for (int i = 1; i <= n; i++)
		a[i] = 1;

	for (int i = 2; i <= n; i++)
		if (a[i]) {count++;
		for (int j = i + i; j <= n; j += i)
			a[j] = 0;
	}
	
	printf("%d", count);

	return 0;
}