/* Problem URL: https://codeforces.com/gym/103388/problem/G */

#include <bits/stdc++.h>

using namespace std;

#define V vector

#define rmin(a, b) a = min(a, b)
#define rmax(a, b) a = max(a, b)

#define rep(i, lim) for (int i = 0; i < (lim); i++)
#define nrep(i, s, lim) for (int i = s; i < (lim); i++)

#define repv(i, v) for (auto &i : (v))
#define fillv(v) for (auto &itr_ : (v)) { cin >> itr_; }
#define sortv(v) sort(v.begin(), v.end())
#define all(v) (v).begin(), (v).end()

using vi = vector<int>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
using vvvvi = vector<vvvi>;

using ll = long long;

using vl = vector<ll>;
using vvl = vector<vl>;
using vvvl = vector<vvl>;
using vvvvl = vector<vvvl>;

template<class v>
auto operator<<(ostream &os, const vector<v> &vec)->ostream& {
    os << vec[0];
    for (size_t i = 1; i < vec.size(); i++) {
        os << ' ' << vec[i];
    }
    os << '\n';
    return os;
}

template<class v>
auto operator>>(istream &is, vector<v> &vec)->istream& {
    for (auto &i : vec) {
        is >> i;
    }
    return is;
}

template<class v>
auto operator<<(ostream &os, const vector<vector<v>> &vec)->ostream& {
    for (auto &i : vec) {
        os << i[0];
        for (size_t j = 1; j < i.size(); j++) {
            os << ' ' << i[j];
        }
        os << '\n';
    }
    return os;
}

template<class v>
auto operator>>(istream  &is, vector<vector<v>> &vec)->istream& {
    for (auto &i : vec) {
        for (auto &j : i) {
            is >> j;
        }
    }
    return is;
}

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    ll n;
    cin >> n;

    vl dp(77);
    dp[0] = 1;
    dp[1] = 1;
    
    rep(i, 75) {
        dp[i + 1] += dp[i];
        dp[i + 2] += dp[i];
    }

    unordered_map<ll, bool> vis;

    vi ans;

    function<bool(ll)> dfs = [&](ll now) {
        if (now == 1) {
            return true;
        }

        if (vis[now]) {
            return false;
        }

        vis[now] = true;

        for (int i = 74; i > 0; i--) {
            if (now % dp[i] == 0) {
                bool res = dfs(now / dp[i]);

                if (res) {
                    ans.push_back(i);
                    return true;
                }
            }
        }

        return false;
    };

    if (!dfs(n)) {
        cout << "IMPOSSIBLE\n";
        return 0;
    }

    reverse(all(ans));

    string tmp;

    repv(i, ans) {
        tmp += string(i, 'A');
        tmp += 'B';
    }

    cout << tmp << '\n';
}