#include <bits/stdc++.h>
using namespace std;
int n, m, k, S, T;
char s[2555];
vector<int> adj[2555];
int val[2555], d[2555], p[2555];
string ans;
void check(int x) {
  string now;
  for (; d[x]; x = p[x]) now += s[x];
  reverse(now.begin(), now.end());
  if (now.length() < ans.length())
    ans = now;
  else if (now.length() == ans.length() && now < ans)
    ans = now;
}
bool cmp_val(int i, int j) { return val[i] < val[j]; }
void solve(int mask) {
  memset(d, -1, sizeof d);
  vector<int> u, v;
  d[S] = 0, val[S] = 0, u.push_back(S);
  while (!u.empty()) {
    v.clear();
    for (int i = 0; i < u.size(); i++) {
      int x = u[i];
      for (int j = 0; j < adj[x].size(); j++) {
        int y = adj[x][j];
        if (y == T) {
          check(x);
          return;
        }
        if (d[y] != -1 || !(mask >> (s[y] - 'a') & 1)) continue;
        d[y] = d[x] + 1, p[y] = x, val[y] = val[x] * 2555 + s[y],
        v.push_back(y);
      }
    }
    sort(v.begin(), v.end(), cmp_val);
    for (int i = 0, prv; i < v.size(); i++) {
      if (i == 0)
        prv = val[v[0]], val[v[0]] = 0;
      else {
        int tmp = val[v[i]];
        val[v[i]] = val[v[i - 1]] + (tmp != prv);
        prv = tmp;
      }
    }
    u = v;
  }
}
bool good(int i, int j) { return 0 <= i && i < n && 0 <= j && j < m; }
int node(int i, int j) { return i * m + j; }
bool cmp_s(int i, int j) { return s[i] < s[j]; }
int main() {
  scanf("%d%d%d", &n, &m, &k);
  for (int i = 0; i < n; i++) scanf("%s", s + i * m);
  ans = string(3000, 'a');
  for (int i = 0; i < n * m; i++) {
    if (s[i] == 'S') S = i;
    if (s[i] == 'T') T = i;
  }
  for (int i = 0; i < n; i++)
    for (int j = 0; j < m; j++) {
      if (good(i + 1, j)) adj[node(i, j)].push_back(node(i + 1, j));
      if (good(i - 1, j)) adj[node(i, j)].push_back(node(i - 1, j));
      if (good(i, j + 1)) adj[node(i, j)].push_back(node(i, j + 1));
      if (good(i, j - 1)) adj[node(i, j)].push_back(node(i, j - 1));
    }
  for (int i = 0; i < n * m; i++) sort(adj[i].begin(), adj[i].end(), cmp_s);
  for (int i = 0; i < (1 << 26); i++)
    if (__builtin_popcount(i) == k) solve(i);
  if (ans.length() == 3000) ans = "-1";
  cout << ans << endl;
}
