#include <bits/stdc++.h>
using namespace std;
int n, m, k;
char mapa[55][55];
pair<int, int> ini, fim;
int dX[] = {1, 0, -1, 0};
int dY[] = {0, -1, 0, 1};
set<int> set_cores[55][55];
struct evento {
  int x, y, cores, dist;
  string caminho;
  evento(int x, int y) : x(x), y(y), cores(0), dist(0), caminho("") {}
  evento(int x, int y, int d, int co, string c)
      : x(x), y(y), cores(co), dist(d), caminho(c) {}
  bool operator<(const evento& o) const {
    return tie(dist, caminho) > tie(o.dist, o.caminho);
  }
};
bool invalid(int nx, int ny) { return nx < 0 || nx >= n || ny < 0 || ny >= m; }
void dijkstra() {
  priority_queue<evento> pfila;
  pfila.push(evento(ini.first, ini.second));
  while (!pfila.empty()) {
    evento u = pfila.top();
    pfila.pop();
    int x = u.x, y = u.y;
    if (mapa[x][y] == 'T') {
      cout << u.caminho << endl;
      return;
    }
    for (int i = 0; i < 4; i++) {
      int nx = x + dX[i];
      int ny = y + dY[i];
      string ncaminho = u.caminho;
      int ncores = u.cores;
      if (invalid(nx, ny)) continue;
      if (mapa[nx][ny] >= 'a' && mapa[nx][ny] <= 'z') {
        ncaminho += mapa[nx][ny];
        ncores |= (1 << (mapa[nx][ny] - 'a'));
      }
      int flag_visitado = 0;
      for (auto cor : set_cores[nx][ny]) {
        if ((cor | ncores) == ncores) {
          flag_visitado = 1;
          break;
        }
      }
      if (flag_visitado) continue;
      if (__builtin_popcount(ncores) <= k) {
        set_cores[nx][ny].insert(ncores);
        pfila.push(evento(nx, ny, u.dist + 1, ncores, ncaminho));
      }
    }
  }
  cout << "-1" << endl;
}
int main() {
  scanf("%d %d %d", &n, &m, &k);
  for (int i = 0; i < n; i++) {
    scanf("%s", mapa[i]);
    for (int j = 0; j < m; j++) {
      if (mapa[i][j] == 'S') {
        ini = {i, j};
      }
      if (mapa[i][j] == 'T') {
        fim = {i, j};
      }
    }
  }
  dijkstra();
  return 0;
}
