#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

#define error(args...) { string _s = #args; replace(_s.begin(), _s.end(), ',', ' '); stringstream _ss(_s); istream_iterator<string> _it(_ss); err(_it, args); }
#define sz(x) (int)x.size()
#define all(x) x.begin(),x.end()
#define gtr(T) vector<T>,greater<T>
#define int long long
using namespace std;
using namespace __gnu_pbds;
template<class T> using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;

void err(istream_iterator<string> it) { cerr << endl; }

template<typename T, typename... Args>
void err(istream_iterator<string> it, T a, Args... args) {
    cerr << *it << " = " << a << endl;
    err(++it, args...);
}

using ll = long long;
using pii = pair<int, int>;
using vi = vector<int>;
using vvi = vector<vector<int>>;
const int N = 2005;
int dp[N][N], n, m;
char a[N][N];

int solve(int r, int c) {
    if (r >= n or c >= m)return 0;
    int &ret = dp[r][c];
    if (~ret)return ret;
    ret = 0;
    if (a[r][c] == 'C')ret = 1;
    ret += max(solve(r + 1, c), solve(r, c + 1));
    return ret;
}

void trace(int r, int c) {
    if (r >= n or c >= m)return;
    if (solve(r + 1, c) > solve(r, c + 1)) {
        a[r][c] = '_';
        trace(r + 1, c);
    } else
        a[r][c] = '_', trace(r, c + 1);
}

signed main() {
    int n;
    cin >> n;
    vector<int> v{1, 3};
    while (v.back() <= n) {
        v.push_back(v.back() * 2 - 1);
    }
    for (auto e: v) {
        if (e > n || find(v.begin(), v.end(), n - e + 1) == v.end()) continue;
        cout << e << endl;
        exit(0);
    }
    cout << "impossible";
}