#include <bits/stdc++.h>
using namespace std;

const int maxn = 1e6 + 15;
bool is_prime[maxn];
int sieve(int x){
	int res = 0;
	fill(is_prime+2,is_prime+x+1,true);
	for(int i = 2; i <= x; i++) if(is_prime[i]){
		res++;
		for(int j = 2 * i; j <= x; j += i) is_prime[j] = false;
	}
	return res;
}

int main(){
	int n;
	while(scanf("%d", &n) == 1) printf("%d\n", sieve(n));
	return 0;
}