#include <bits/stdc++.h>
using namespace std;
char str[52][52];
int road[52][52];
int n, m, k;
int sx, sy, ex, ey;
int able[52 * 52];
string bst;
int sequence[52 * 52 * 8];
int afk[52][52];
int vis[52][52];
pair<int, int> pre[52][52];
int ax[] = {-1, 1, 0, 0}, ay[] = {0, 0, -1, 1};
void trysolve() {
  memset(vis, 0x3f, sizeof vis);
  memset(afk, 0x3f, sizeof afk);
  queue<pair<int, int> > q[2];
  int now = 0;
  vis[sx][sy] = 1;
  q[now].push(make_pair(sx, sy));
  afk[sx][sy] = 1;
  while (q[now].size() and vis[ex][ey] > 1e8) {
    vector<pair<int, int> > all;
    while (q[now].size()) {
      int x = q[now].front().first, y = q[now].front().second;
      q[now].pop();
      for (int i = 0; i < 4; i++) {
        int tx = x + ax[i], ty = y + ay[i];
        if (str[tx][ty] != 'T' and !able[road[tx][ty]]) continue;
        int ene = afk[x][y] * 5 + able[road[tx][ty]];
        if (vis[tx][ty] > vis[x][y] + 1) {
          vis[tx][ty] = vis[x][y] + 1;
          afk[tx][ty] = ene;
          all.push_back(make_pair(tx, ty));
          pre[tx][ty] = make_pair(x, y);
        } else if (vis[tx][ty] == vis[x][y] + 1 and afk[tx][ty] > ene) {
          afk[tx][ty] = ene;
          pre[tx][ty] = make_pair(x, y);
        }
      }
    }
    int upp = 0;
    for (int i = 0; i < all.size(); i++)
      sequence[afk[all[i].first][all[i].second]] = 1,
      upp = max(upp, afk[all[i].first][all[i].second]);
    int tot = 0;
    for (int i = 1; i <= upp; i++)
      if (sequence[i]) sequence[i] = ++tot;
    for (int i = 0; i < all.size(); i++)
      afk[all[i].first][all[i].second] =
          sequence[afk[all[i].first][all[i].second]];
    for (int i = 1; i <= upp; i++)
      if (sequence[i]) sequence[i] = 0;
    now ^= 1;
    for (int i = 0; i < all.size(); i++) q[now].push(all[i]);
  }
  if (vis[ex][ey] < 1e8) {
    int x = pre[ex][ey].first, y = pre[ex][ey].second;
    string gg;
    while (x != sx or y != sy) {
      gg += char('a' - 1 + road[x][y]);
      pair<int, int> op = pre[x][y];
      x = op.first, y = op.second;
    }
    reverse(gg.begin(), gg.end());
    if (bst.size() > gg.size()) bst = gg;
    if (bst.size() == gg.size()) bst = min(bst, gg);
  }
}
void solve(int xk, int cnt) {
  if (cnt > k) return;
  if (xk == 27) trysolve();
  if (xk == 27) return;
  solve(xk + 1, cnt);
  able[xk] = cnt + 1;
  solve(xk + 1, cnt + 1);
  able[xk] = 0;
}
signed main() {
  scanf("%d%d%d", &n, &m, &k);
  for (int i = 1; i <= n; i++) scanf("%s", str[i] + 1);
  for (int i = 1; i <= n; i++)
    for (int j = 1; j <= m; j++) {
      if (str[i][j] == 'S') sx = i, sy = j;
      if (str[i][j] == 'T') ex = i, ey = j;
      bst += 'o';
    }
  for (int i = 1; i <= n; i++)
    for (int j = 1; j <= m; j++) road[i][j] = str[i][j] - 'a' + 1;
  solve(1, 0);
  if (bst.size() >= n * m) bst = "-1";
  cout << bst;
  return 0;
}
