#include <bits/stdc++.h> //JuniorMonster a.k.a Sho10
#define ll long long int
#pragma GCC optimize("O3")
#pragma GCC optimize("Ofast")
#define all(a) (a).begin(), (a).end()
#define sz size
#define f first
#define s second
#define pb push_back
#define er erase
#define in insert
#define mp make_pair
#define pi pair
#define rc(s) return cout<<s,0
#define mod 1000000007
#define PI 3.14159265359
#define CODE_START  ios_base::sync_with_stdio(false);cin.tie(0);cerr.tie(0);cout.tie(0);
using namespace std;
ll n,ans=0;
int32_t main(){
ifstream cin("ciur.in");
ofstream cout("ciur.out");
CODE_START;
cin>>n;
char viz[n+5];
for(ll i=2;i<=n;i++)
{
    viz[i]=1;
}
for(ll i=2;i<=n;i++)
if(viz[i]==1){
    ans++;
for(ll j=2*i;j<=n;j=j+i)
viz[j]=0;
}
cout<<ans<<endl;
}