#include <algorithm>
#include <iostream>

bool judge1(long long int n) {
    for(int i = 0;i <= 60;++i) {
        if ((1ll << i) + 1 == n) {
            return true;
        }
    }
    return false;
}

bool judge2(long long int n) {
    for(int i = 0;i <= 60;++i) {
        for(int j = i + 1;j <= 60;++j) {
            if ((1ll << i) + (1ll << j) + 1 == n) {
                return true;
            }
        }
    }
    return false;
}

void solve() {
    long long int n;
    std::cin >> n;
    if (n <= 3) {
        std::cout << "1\n";
        return;
    }
    if (judge1(n)) {
        std::cout << (n / 2) + 1 << "\n";
    } else if (judge2(n)) {
        n -= 1;
        // 找第一个 1 位置
        std::cout << (n & (-n)) + 1 << "\n";
    } else {
        std::cout << "impossible\n";
    }
}

int main() {
    solve();
    return 0;
}