#include <stdio.h>

#define nm 2000100

int n, sol;
char v[nm];

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

	scanf("%d", &n);

	for (int i = 2; i <= n; ++i)
		if (!v[i]) {
			++sol;

			for (int j = i + i; j <= n; j += i)
				v[j] = 1;
		}

	printf("%d\n", sol);

	return 0;
}