#include <bits/stdc++.h>
#define endl '\n'
#define x first
#define y second
#define stop cout << "?" << '\n'
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<long long, long long> pll;
const int N = 2e2 + 100, M = 1000;
const ll mod = 1e9 + 7;
const double pi = acos(-1);
char ans[N][N];
int n, m, k;
int h, w, sz;
void change(int n, int m)
{
    for (int i = 1; i <= sz; i++)
        if (sz % i == 0)
        {
            if (sz / i <= n && i <= m && m % i == 0)
            {
                h = sz / i, w = i;
                break;
            }
        }
}
void solve()
{
    cin >> n >> m >> k;
    if ((n * m) % k)
    {
        cout << "impossible" << endl;
        return;
    }
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= m; j++)
            ans[i][j] = '#';
    sz = n * m / k;
    change(n, m);
    int cnt = 0;
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= m; j++)
            if (i + h - 1 <= n && j + w - 1 <= m && ans[i][j] == '#')
            {
                // cout << i + h - 1 << " " << j + w - 1 << endl;
                for (int v = i; v <= i + h - 1; v++)
                    for (int u = j; u <= j + w - 1; u++)
                        ans[v][u] = char('A' + cnt);
                cnt++;
            }
    while (cnt < k)
    {

        int nn = -1, nm = -1;
        for (int i = 1; i <= n; i++)
        {
            if (nn != -1)
                break;
            for (int j = 1; j <= m; j++)
                if (ans[i][j] == '#')
                {
                    nn = n - i + 1;
                    nm = m - j + 1;
                    break;
                }
        }
        change(nn, nm);
        // cout << nn << " " << nm << endl;
        // cout << h << " " << w << endl;
        for (int i = 1; i <= n; i++)
            for (int j = 1; j <= m; j++)
            {
                if (i + h - 1 <= n && j + w - 1 <= m && ans[i][j] == '#')
                {
                    for (int v = i; v <= i + h - 1; v++)
                        for (int u = j; u <= j + w - 1; u++)
                            ans[v][u] = char('A' + cnt);
                    cnt++;
                }
            }
    }
    for (int i = 1; i <= n; i++)
    {
        for (int j = 1; j <= m; j++)
            cout << ans[i][j];
        cout << endl;
    }
}
int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    int _ = 1;
    // cin >> _;
    while (_--)
        solve();
    return 0;
}