#include <bits/stdc++.h>

using namespace std;

int main() {
    string zoo;
    cin >> zoo;
    int cnt = 1, cnt2 = 1;

    map<int, int> answer;
    stack<pair<char, int>> v;
    vector<int> idx(zoo.length()), ans;

    for(int i = 0; i < zoo.length(); ++i){
        if(zoo[i] >= 'a' && zoo[i] <= 'z'){
            idx[i] = cnt;
            cnt++;
        }else{
            idx[i] = cnt2;
            cnt2++;
        }
    }

    for(int i = 0; i < zoo.length(); ++i){
        if(v.empty()){
            v.push({zoo[i], idx[i]});

        }else if(v.top().first - 'a' == zoo[i] - 'A'){
            if(v.top().first >= 'A' && v.top().first <= 'Z'){
                answer[v.top().second] = idx[i];
            }else{
                answer[idx[i]] = v.top().second;
            }

            v.pop();
        }else if (v.top().first - 'A' == zoo[i] - 'a'){
            if(v.top().first >= 'A' && v.top().first <= 'Z'){
                answer[v.top().second] = idx[i];
            }else{
                answer[idx[i]] = v.top().second;
            }

            v.pop();
        }else{
            v.push({zoo[i], idx[i]});
        }
    }

    if(v.empty()){
        cout << "Possible\n";
        for(auto el : answer){
            cout << el.second << ' ';
        }
    }else{
        cout << "Impossible\n";
    }

}