#include <cstdio>
#include <cmath>

using namespace std;

const int MAXN = 100000000;

bool notPrime[MAXN + 1];
int primes[MAXN];

int sieve(int n) {
	int primesCount = 0;
	int sqrt_n = (int)sqrt((double)n);
	primes[primesCount++] = 2;
	int i = 3;
	while (i <= sqrt_n) {
		if (!notPrime[i]) {
			primes[primesCount++] = i;
			int i_2 = i << 1;
			for (int j = i * i; j <= n; j += i_2) {
				notPrime[j] = true;
			}
		}
		i += 2;
	}
	while (i <= n) {
		if (!notPrime[i]) {
			primes[primesCount++] = i;
		}
		i += 2;
	}
	return primesCount;
}

int main() {
	int n; scanf("%d", &n);
	printf("%d\n", sieve(n));
	return 0;
}