#include <bits/stdc++.h>
using namespace std;
vector<string> mat;
int dx[] = {0, 0, 1, -1};
int dy[] = {1, -1, 0, 0};
long long d(long long x1, long long x2, long long y1, long long y2) {
  return (abs(y2 - y1) + abs(x2 - x1));
}
int main() {
  long long n, m, k, sx, sy, gx, gy;
  cin >> n >> m >> k;
  string tmp;
  for (int i = 0; i < n; i++) {
    cin >> tmp;
    mat.push_back(tmp);
    for (int j = 0; j < m; j++) {
      if (mat[i][j] == 'S') {
        sy = i;
        sx = j;
      } else if (mat[i][j] == 'T') {
        gy = i;
        gx = j;
      }
    }
  }
  priority_queue<
      pair<long long, pair<pair<string, long long>, long long> >,
      vector<pair<long long, pair<pair<string, long long>, long long> > >,
      greater<pair<long long, pair<pair<string, long long>, long long> > > >
      pq;
  set<pair<long long, long long> > ss;
  pq.push(
      make_pair(d(sx, gx, sy, gy), make_pair(make_pair("", 0), sy * m + sx)));
  while (!pq.empty()) {
    long long an = pq.top().second.second;
    long long ay = pq.top().second.second / m;
    long long ax = pq.top().second.second % m;
    string astr = pq.top().second.first.first;
    long long mask = pq.top().second.first.second;
    pq.pop();
    if (ss.count(make_pair(mask, an))) continue;
    ss.insert(make_pair(mask, an));
    for (int i = 0; i < 4; i++) {
      int nx = ax + dx[i];
      int ny = ay + dy[i];
      if (ny < 0 || ny >= n || nx < 0 || nx >= m) continue;
      if (ny == gy && nx == gx) {
        cout << astr << endl;
        return 0;
      }
      string nstr = astr + mat[ny][nx];
      long long nmask = mask | (1 << (mat[ny][nx] - 'a'));
      if (__builtin_popcount(nmask) <= k)
        pq.push(make_pair(d(nx, gx, ny, gy) + nstr.size(),
                          make_pair(make_pair(nstr, nmask), ny * m + nx)));
    }
  }
  cout << "-1" << endl;
}
