#include <stdio.h>
#include <math.h>

int primes[78498], num_primes;
int calculated;
int count_pos(int n) {
	for (int i = 0; i < num_primes; i++) {
		if (primes[i] == n) {
			return i + 1;
		}
		else if (primes[i] > n) {
			return i;
		}
	}
	return num_primes;
}
int main() {
	primes[0] = 2;
	calculated = 2;
	num_primes = 1;
	while (true) {
		int n;
		if (!scanf("%d", &n)) break;
		if (calculated+1 < n) {
			for (int i = calculated + 1; i < n + 1; i += 2) {
				bool is_prime = true;
				int max = (int)(sqrt(i)) + 1;
				for (int j=1; primes[j] < max&&j<num_primes; j++) {
					if (i%primes[j] == 0) {
						is_prime = false;
						break;
					}
				}
				if (is_prime) {
					primes[num_primes++] = i;
				}
			}
			calculated = n - (n % 2);
		}
		printf("%d\n", count_pos(n));
	}
}
