#include <stdio.h>

char sieve[2000001];

int main () {
	freopen("ciur.in", "r", stdin);
	freopen("ciur.out", "w", stdout);
	long n, i, j; scanf("%ld", &n);
	long k = 0;
	for(i = 2; i <= n; i++) sieve[i] = 1;
	for(i = 2; i <= n; i++)
		if(sieve[i] == 1) {
			k++;
			for(j = i * i; j <= n; j+=i)
				sieve[j] = 0;
		}
	printf("%ld", k);
	return 0;
}