#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define debug(a) cout << #a << "-->" << (a) << '\n';

int main()
{
    ios ::sync_with_stdio(false);
    cin.tie(NULL);
    int n;
    cin>>n;
    if(n%2==0)
    {
        cout<<n-2<<'\n';
    }
    else{
        cout<<n-1<<'\n';
    }
    return 0;
}