#include <iostream>
#include <bitset>
#define MAX 2000002

using namespace std;

bitset<MAX> prime;
int n, cnt;

int main(){
	prime.set();
	int i, j;
	//freopen("ciur.in", "r", stdin);
	//freopen("ciur.out", "w", stdout);
	scanf("%d", &n);
	for(i = 2; i <= n; i++){
		if(prime[i]){
			cnt++;
			for(j = i + i; j <= n; j+=i){
				prime[j] = 0;
			}
		}
	}
	printf("%d\n", cnt);
	return 0;
}