#include using namespace std; typedef vector VI; typedef vector VVI; typedef vector VS; typedef pair PII; typedef pair pii; typedef pair PLL; typedef pair TIII; typedef long long ll; typedef long double ld; typedef unsigned long long ull; #define FOR(i, s, n) for (int i = s; i < (int)n; ++i) #define REP(i, n) FOR(i, 0, n) #define rep(i, a, b) for (int i = a; i < (b); ++i) #define trav(a, x) for (auto &a : x) #define all(x) x.begin(), x.end() #define MOD 1000000007 template inline bool chmax(T1 &a, T2 b) {if (a < b) {a = b; return true;} return false;} template inline bool chmin(T1 &a, T2 b) {if (a > b) {a = b; return true;} return false;} const double EPS = 1e-12, PI = acos(-1); const double pi = 3.141592653589793238462643383279; typedef string::const_iterator State; ll GCD(ll a, ll b){ return (b==0)?a:GCD(b, a%b); } ll LCM(ll a, ll b){ return a/GCD(a, b) * b; } template< int mod > struct ModInt { int x; ModInt() : x(0) {} ModInt(int64_t y) : x(y >= 0 ? y % mod : (mod - (-y) % mod) % mod) {} ModInt &operator+=(const ModInt &p) { if((x += p.x) >= mod) x -= mod; return *this; } ModInt &operator-=(const ModInt &p) { if((x += mod - p.x) >= mod) x -= mod; return *this; } ModInt &operator*=(const ModInt &p) { x = (int) (1LL * x * p.x % mod); return *this; } ModInt &operator/=(const ModInt &p) { *this *= p.inverse(); return *this; } ModInt operator-() const { return ModInt(-x); } ModInt operator+(const ModInt &p) const { return ModInt(*this) += p; } ModInt operator-(const ModInt &p) const { return ModInt(*this) -= p; } ModInt operator*(const ModInt &p) const { return ModInt(*this) *= p; } ModInt operator/(const ModInt &p) const { return ModInt(*this) /= p; } bool operator==(const ModInt &p) const { return x == p.x; } bool operator!=(const ModInt &p) const { return x != p.x; } ModInt inverse() const { int a = x, b = mod, u = 1, v = 0, t; while(b > 0) { t = a / b; swap(a -= t * b, b); swap(u -= t * v, v); } return ModInt(u); } ModInt pow(int64_t n) const { ModInt ret(1), mul(x); while(n > 0) { if(n & 1) ret *= mul; mul *= mul; n >>= 1; } return ret; } friend ostream &operator<<(ostream &os, const ModInt &p) { return os << p.x; } friend istream &operator>>(istream &is, ModInt &a) { int64_t t; is >> t; a = ModInt< mod >(t); return (is); } static int get_mod() { return mod; } }; using modint = ModInt< 1000000007 >; template< typename T > struct Combination { vector< T > _fact, _rfact, _inv; Combination(int sz) : _fact(sz + 1), _rfact(sz + 1), _inv(sz + 1) { _fact[0] = _rfact[sz] = _inv[0] = 1; for(int i = 1; i <= sz; i++) _fact[i] = _fact[i - 1] * i; _rfact[sz] /= _fact[sz]; for(int i = sz - 1; i >= 0; i--) _rfact[i] = _rfact[i + 1] * (i + 1); for(int i = 1; i <= sz; i++) _inv[i] = _rfact[i] * _fact[i - 1]; } inline T fact(int k) const { return _fact[k]; } inline T rfact(int k) const { return _rfact[k]; } inline T inv(int k) const { return _inv[k]; } T P(int n, int r) const { if(r < 0 || n < r) return 0; return fact(n) * rfact(n - r); } T C(int p, int q) const { if(q < 0 || p < q) return 0; return fact(p) * rfact(q) * rfact(p - q); } T H(int n, int r) const { if(n < 0 || r < 0) return (0); return r == 0 ? 1 : C(n + r - 1, r); } }; ll modpow(ll x, ll n, ll mod) { ll res = 1; while(n) { if(n&1) res = (res * x) % mod; x = (x * x) % mod; n >>= 1; } return res; } typedef vector vec; typedef vector mat; mat mul(mat &A, mat &B){ mat C(A.size(), vec(B[0].size())); for(int i=0; i 0){ if(n&1) B = mul(B, A); A = mul(A, A); n >>= 1; } return B; } inline long long mod(long long a, long long m) { return (a % m + m) % m; } int main() { cin.tie(0); ios::sync_with_stdio(false); cout << fixed << setprecision(12); ll X; cin >> X; vector v; ll t = X; while(t){ v.push_back(t%2); t/=2; } reverse(all(v)); for(ll i=1; i<=v.size(); i++) { //bitの本数がiでX^i=Nであるような数が存在するか ll N = X^i; ll tar = 0; ll now = 0; for(int j=0; j N) continue; now += (1LL<<(v.size()-1-j)); tar++; } if(tar == i && now == N) { cout << N << endl; return 0; } } cout << -1 << endl; return 0; }