#include <bits/stdc++.h>
#define fi first
#define se second
#define rep(i,s,n) for (int i = (s); i < (n); ++i)
#define rrep(i,n,g) for (int i = (n)-1; i >= (g); --i)
#define all(a) a.begin(),a.end()
#define rall(a) a.rbegin(),a.rend()
#define len(x) (int)(x).size()
#define dup(x,y) (((x)+(y)-1)/(y))
#define pb push_back
#define eb emplace_back
#define Field(T) vector<vector<T>>
using namespace std;
using ll = long long;
using ull = unsigned long long;
template<typename T> using pq = priority_queue<T,vector<T>,greater<T>>;
using P = pair<int,int>;
template<class T>bool chmax(T&a,T b){if(a<b){a=b;return 1;}return 0;}
template<class T>bool chmin(T&a,T b){if(b<a){a=b;return 1;}return 0;}

int dx[4] = {1, 0, -1, 0};
int dy[4] = {0, 1, 0, -1};

int main() {
  int h, w, m;
  cin >> h >> w >> m;
  vector<string> s(h);
  rep(i,0,h) cin >> s[i];
  vector<vector<vector<int>>> dist(h, vector<vector<int>>(w, vector<int>(m+1, -1)));
  int si, sj, gi, gj;
  rep(i,0,h) rep(j,0,w) {
    if (s[i][j] == 'S') si = i, sj = j;
    if (s[i][j] == 'G') gi = i, gj = j;
  }
  queue<pair<P,int>> que;
  que.emplace(P{si, sj}, m);
  dist[si][sj][m] = 0;
  while(!que.empty()) {
    P p; int k;
    tie(p, k) = que.front();
    que.pop();
    int x = p.fi, y = p.se;
    // cout << x << " " << y << endl;
    rep(d,0,4) {
      int nx = x+dx[d], ny = y+dy[d];
      if (nx < 0 || nx >= h || ny < 0 || ny >= w) continue;
      if (s[nx][ny] == '#') continue;
      if ('a' <= s[nx][ny] && s[nx][ny] <= 'i') {
        if (s[nx][ny]-'a' != k) continue;
        if (dist[nx][ny][k] == -1) {
          dist[nx][ny][k] = dist[x][y][k]+1;
          que.emplace(P{nx, ny}, k);
        } 
      } else if ('1' <= s[nx][ny] && s[nx][ny] <= '9') {
        int nk = s[nx][ny]-'1';
        if (dist[nx][ny][nk] == -1) {
          dist[nx][ny][nk] = dist[x][y][k]+1;
          que.emplace(P{nx, ny}, nk);
        }
      } else {
        if (dist[nx][ny][k] == -1) {
          dist[nx][ny][k] = dist[x][y][k]+1;
          que.emplace(P{nx, ny}, k);
        }
      }
    }
  }
  int ans = 1000000000;
  rep(k,0,m+1) if (dist[gi][gj][k] != -1) ans = min(ans, dist[gi][gj][k]);
  if (ans == 1000000000) ans = -1;
  cout << ans << endl;
  return 0;
}