#include <bits/stdc++.h>

const int inf=2e9+3;

using namespace std;

int main()
{
    ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);

    int n;
    cin>>n;
    vector<bool>f(n+3,0);
    int ans=0;
    for(int i=2;i<=n;i++)
    if(!f[i])
    {
      ans++;
      for(int j=i*2;j<=n;j+=i) f[j]=1;
    }
    cout<<ans;

}