#include<stdio.h>
int prime[1000000];
int main() {
	prime[0] = -1;
	prime[1] = -1;
	for (int i = 2; i<1000000; i++) {
		if (prime[i] == 0) {
			prime[i] = 1;
			for (int j = i * 2; j<1000000; j += i)prime[j] = -1;
		}
	}
	int now;
	while (~scanf("%d", &now)) {
		int ans = 0;
		for (int i = 1; i<now + 1; i++)if (prime[i] == 1)ans++;
		printf("%d\n", ans);
	}
}
