408.cpp

#include <iostream>
#include <vector>
#include <cstring>

using namespace std;

string trim(const string & s) {
    int l = 0, r = (int) s.size()-1;
    while (isspace(s[l])) ++l;
    while (isspace(s[r])) --r;
    return s.substr(l, r-l+1);
}

int main() {
    setlocale(LC_ALL, ".1251");

    freopen("input.txt", "rt", stdin);
    freopen("output.txt", "wt", stdout);

    int k, n;
    scanf("%d %d\n", &k, &n);

    vector<string> v(n);

    bool flag = 1;

    for (auto & s : v) {
        getline(cin, s);
        s = trim(s);
        flag &= s.size() <= k;
    }

    if (flag) {
        for (int i = 0; i < n; ++i ){
            int countSpaces = k - (int)v[i].size();
            int leftSpaces = countSpaces / 2;
            int rightSpaces = countSpaces - leftSpaces;
            if (i) cout << endl;
            cout << string(leftSpaces, ' ')+v[i]+string(rightSpaces, ' ');
        }
    } else {
        cout << "Impossible.";
    }

    return 0;
}