#include <cstdio>

#define MAXN 2000005

int N;
char Compus[MAXN];

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

	scanf("%d", &N);

	for (int i = 2; i*i <= N; ++i)
		if (!Compus[i])
			for (int j = i*i; j <= N; j += i)
				Compus[j] = 1;

	int ret = 0;
	for (int i = 2; i <= N; ++i)
		ret += !Compus[i];
	printf("%d\n", ret);
}