#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);
	for (int i = 2; i <= n; ++i) {
		if (!notPrime[i]) {
			primes[primesCount++] = i;
			if (i <= sqrt_n) {
				for (int j = i * i; j <= n; j += i) {
					notPrime[j] = true;
				}
			}
		}
	}
	return primesCount;
}

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