#include "bits/stdc++.h"
//#include "atcoder/all"
using namespace std;
//using namespace atcoder;
//using mint = modint1000000007;
//const int mod = 1000000007;
//using mint = modint998244353;
//const int mod = 998244353;
//const int INF = 1e9;
//const long long LINF = 1e18;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep2(i,l,r)for(int i=(l);i<(r);++i)
#define rrep(i, n) for (int i = (n-1); i >= 0; --i)
#define rrep2(i,l,r)for(int i=(r-1);i>=(l);--i)
#define all(x) (x).begin(),(x).end()
#define allR(x) (x).rbegin(),(x).rend()
#define endl "\n"
int popcount(long long n) {
	n = (n & 0x5555555555555555) + (n >> 1 & 0x5555555555555555);
	n = (n & 0x3333333333333333) + (n >> 2 & 0x3333333333333333);
	n = (n & 0x0f0f0f0f0f0f0f0f) + (n >> 4 & 0x0f0f0f0f0f0f0f0f);
	n = (n & 0x00ff00ff00ff00ff) + (n >> 8 & 0x00ff00ff00ff00ff);
	n = (n & 0x0000ffff0000ffff) + (n >> 16 & 0x0000ffff0000ffff);
	n = (n & 0x00000000ffffffff) + (n >> 32 & 0x00000000ffffffff);
	return n;
}
int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	long long X;
	cin >> X;
	long long ans = -1;
	{//M==1
		long long N = X ^ 1;
		if (1 == popcount(N)) { ans = N; }
	}
	{//M==2
		long long N = X ^ 2;
		if (2 == popcount(N)) { ans = N; }
	}
	{//M>=3
		long long nowM = 2;
		long long now2 = 2;
		while (now2 <= X / 2) {
			now2 *= 2;
			nowM++;
			long long N = X ^ nowM;
			if (nowM == popcount(N)) { ans = N; }
		}
	}
	cout << ans << endl;
	return 0;
}