#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define double long double;
#define pb push_back
#define endl '\n'
#define er erase
#define sz size
#define in insert
#define mp make_pair
#define fs first
#define sc second
#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()
#define mod 1000000007
#define INF LONG_LONG_MAX

int n;
vector<bool> primes(2000005, 1);

void ciur(int n)
{
    for(int i=2;i<=n;i++)
    {
        if(primes[i]==1)
        {
            for(int j=i+i;j<=n;j+=i)
            {
                primes[j]=0;
            }
        }
    }
}

ifstream fin("ciur.in");
ofstream fout("ciur.out");

void solve()
{
    fin>>n;
    ciur(n);
    int ans=0;
    for(ll i=2;i<=n;i++)
    if(primes[i]==1){ans++;}
    fout<<ans<<endl;
}

int32_t main()
{
    //ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);
    ll tc=1;
    //cin>>tc;
    while(tc--)
    {
        solve();
    }
    return 0;
}