1. #include <bits/stdc++.h>
2. typedef long long ll;
3. #define FOR(i,l,r) for (int i=l;i<=r;i++)
4. #define FOD(i,r,l) for (int i=r;i>=l;i--)
5. #define fast ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
6. #define pub push_back
7. #define pob pop_back
8. #define ii pair<int,int>
9. #define pll pair<long long, long long>
10. #define F first
11. #define S second
12. typedef unsigned long long int ull;
13. using namespace std;
14. const int N = 1e6+5;
15.  
16. ll n;
17. bool isPrime[N];
18.  
19. void sieve(){
20.     for(int i = 0; i <= N;++i) {
21.         isPrime[i] = true;
22.     }
23.     isPrime[0] = false;
24.     isPrime[1] = false;
25.     for(int i = 2; i * i <= N; ++i) {
26.          if(isPrime[i] == true) {
27.              for(int j = i * i; j <= N; j += i)
28.                  isPrime[j] = false;
29.         }
30.     }
31. }
32.  
33. void solve(){
34.     cin >> n;
35.     sieve();
36.     ll d = 0;
37.     ll p = sqrt(sqrt(n));
38.     FOR(i,1,p) if (isPrime[i]) ++d;
39.     cout << d;
40. }
41.  
42. int main(){
43.     fast;
44.     freopen("BEAUNUM.inp","r",stdin);
45.     freopen("BEAUNUM.out","w",stdout);
46.     solve();
47.     return 0;
48. }
49.