Language: C++

#include <bits/stdc++.h>

#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define FOR(i,n,m) for(int i=(int)(n); i<=(int)(m); i++)
#define RFOR(i,n,m) for(int i=(int)(n); i>=(int)(m); i--)
#define ITR(x,c) for(__typeof(c.begin()) x=c.begin();x!=c.end();x++)
#define RITR(x,c) for(__typeof(c.rbegin()) x=c.rbegin();x!=c.rend();x++)
#define setp(n) fixed << setprecision(n)

template<class T> bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T> bool chmin(T &a, const T &b) { if (a>b) { a=b; return 1; } return 0; }

#define ll long long
#define vll vector<ll>
#define vi vector<int>
#define pll pair<ll,ll>
#define pi pair<int,int>

#define all(a) (a.begin()),(a.end())
#define rall(a) (a.rbegin()),(a.rend())
#define fi first
#define se second
#define pb push_back
#define ins insert

#define debug(a) cerr<<(a)<<endl
#define dbrep(a,n) rep(_i,n) cerr<<(a[_i])<<" "; cerr<<endl
#define dbrep2(a,n,m) rep(_i,n){rep(_j,m) cerr<<(a[_i][_j])<<" "; cerr<<endl;}

using namespace std;

template<class A, class B>
ostream &operator<<(ostream &os, const pair<A,B> &p){return os<<"("<<p.fi<<","<<p.se<<")";}
template<class A, class B>
istream &operator>>(istream &is, pair<A,B> &p){return is>>p.fi>>p.se;}

//-------------------------------------------------
//--Enum various numbers
//-------------------------------------------------
namespace Enum
{
    using fint = ::std::int_fast64_t;
    //素因数分解(素因数列挙)
    ::std::map<fint,int> factor(fint n)
    {
        ::std::map<fint,int> ret;
        for(fint i=2; i*i<=n; i++){
            while(n%i==0){
                ret[i]++;
                n/=i;
            }
        }
        if (n!=1) ret[n]++;
        return ret;
    }
    //約数列挙
    ::std::vector<fint> divisor(fint n)
    {
        ::std::vector<fint> ret;
        for(fint i=1; i*i<=n; i++){
            if (n%i==0){
                ret.push_back(i);
                if (i*i!=n) ret.push_back(n/i);
            }
        }
        return ret;
    }
    //商列挙(割る最小の数と商のペア)
    ::std::vector<::std::pair<fint,fint> > quotient(fint n)
    {
        ::std::vector<::std::pair<fint,fint> > ret;
        fint i=0;
        for(i=1; i*i<=n; i++){
            ret.emplace_back(i,n/i);
        }
        for(; i<=n; i++){
            fint d = n/i;
            ret.emplace_back(i,d);
            i+=(n-d*i)/d;
        }
        return ret;
    }
    //素数判定(おまけ)
    bool isprime(fint n)
    {
        for(fint i=2; i*i<=n; i++){
            if (n%i==0) return false;
        }
        return true;
    }
}

//-------------------------------------------------
//--Extended GCD
//-------------------------------------------------

int_fast64_t extgcd(int_fast64_t a, int_fast64_t b, int_fast64_t &x, int_fast64_t &y)
{
    if (b==0){
        x = 1; y = 0;
        return a;
    }
    int_fast64_t d = extgcd(b,a%b,y,x);
    y -= a/b*x;
    return d;
}

//-------------------------------------------------

int main(void)
{
    cin.tie(0);
    ios::sync_with_stdio(false);
    ll N; cin>>N;
    auto fac = Enum::factor(N*2);
    vll fs;
    for(auto f:fac){
        ll m=1LL;
        rep(i,f.se) m*=f.fi;
        fs.pb(m);
    }
    ll ans=N*2-1;
    int F = fs.size();
    rep(S,1<<F){
        ll A=1LL, B=1LL;
        rep(i,F)if(S>>i&1){
            A*=fs[i];
        }
        rep(i,F)if(!(S>>i&1)){
            B*=fs[i];
        }
        if (A==1LL||B==1LL) continue;
        ll x,y;
        extgcd(A,-B,x,y);
        chmin(ans,min(abs(A*x),abs(B*y)));
    }
    cout<<ans<<endl;
    return 0;
}


Compiler output:
a.cc: In function 'int main()':
a.cc:134:21: error: cannot bind non-const lvalue reference of type 'int_fast64_t&' {aka 'long int&'} to a value of type 'long long int'
  134 |         extgcd(A,-B,x,y);
      |                     ^
a.cc:97:67: note:   initializing argument 3 of 'int_fast64_t extgcd(int_fast64_t, int_fast64_t, int_fast64_t&, int_fast64_t&)'
   97 | int_fast64_t extgcd(int_fast64_t a, int_fast64_t b, int_fast64_t &x, int_fast64_t &y)
      |                                                     ~~~~~~~~~~~~~~^