#include <bits/stdc++.h>
using namespace std;
const int dx[] = {0, 0, 1, -1};
const int dy[] = {1, -1, 0, 0};
int N, M, K;
int F[60][60], Q[3000][2];
int SX, SY, TX, TY;
string P[60][60];
pair<char, int> A[4];
string Ret;
char Map[60][60];
bool G[60][60], Choose[30];
inline void BFS() {
  memset(G, false, sizeof(G));
  for (int i = 1; i <= N; i++) {
    for (int j = 1; j <= M; j++)
      if (Choose[Map[i][j] - 'a']) {
        G[i][j] = true;
      }
  }
  G[SX][SY] = true;
  G[TX][TY] = true;
  memset(F, -1, sizeof(F));
  F[SX][SY] = 0;
  int Head = 0, Tail = 1;
  Q[1][0] = SX;
  Q[1][1] = SY;
  while (Head++ < Tail) {
    int x = Q[Head][0];
    int y = Q[Head][1];
    if (x == TX && y == TY) {
      break;
    }
    if (x != SX || y != SY) {
      P[x][y] += Map[x][y];
    }
    for (int i = 0; i < 4; i++) {
      int u = x + dx[i];
      int v = y + dy[i];
      if (!G[u][v]) {
        continue;
      }
      if (F[u][v] == -1) {
        F[u][v] = F[x][y] + 1;
        P[u][v] = P[x][y];
        Tail++;
        Q[Tail][0] = u;
        Q[Tail][1] = v;
      } else if (F[x][y] + 1 == F[u][v] && P[x][y] < P[u][v]) {
        P[u][v] = P[x][y];
      }
    }
  }
  if (F[TX][TY] == -1) {
    return;
  }
  if (Ret != "-1" && F[TX][TY] > Ret.size() + 1) {
    return;
  }
  string Ans = P[TX][TY];
  if (Ret == "-1" || Ans.size() < Ret.size() || Ans < Ret) {
    Ret = Ans;
  }
}
inline void Search(int k, int total) {
  if (total > K) {
    return;
  }
  if (k == 26) {
    if (total == K) {
      BFS();
    }
  } else {
    Choose[k] = true;
    Search(k + 1, total + 1);
    Choose[k] = false;
    Search(k + 1, total);
  }
}
int main(int argc, char *argv[]) {
  scanf("%d%d%d", &N, &M, &K);
  for (int i = 1; i <= N; i++) {
    scanf("%s", Map[i] + 1);
    for (int j = 1; j <= M; j++) {
      if (Map[i][j] == 'S') {
        SX = i;
        SY = j;
        Map[i][j] = 'a';
      }
      if (Map[i][j] == 'T') {
        TX = i;
        TY = j;
        Map[i][j] = 'a';
      }
    }
  }
  Ret = "-1";
  Search(0, 0);
  cout << Ret << endl;
  return 0;
}
