#if __has_include(<yoniha/all.h>)
#include <yoniha/all.h>
using namespace atcoder;
#else
#include <bits/stdc++.h>
#if __has_include(<atcoder/all>)
#include <atcoder/all>
using namespace atcoder;
#endif
#endif
using namespace std;

#define int long long
#define all(x) (x).begin(), (x).end()
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define rrep(i, n) for(int i = (int)(n - 1); i >= 0; i--)
template <typename T> bool chmax(T &a,const T &b){if(a<b){a=b;return true;}return false;}
template <typename T> bool chmin(T &a,const T &b){if(a>b){a=b;return true;}return false;}

// using mint = modint;

signed main(){
  int h, w, m; cin >> h >> w >> m;
  vector<string> s(h); for(auto&& si : s) cin >> si;
  
  int si, sj, gi, gj;
  rep(i, h) rep(j, w){
  	if(s.at(i).at(j) == 'S'){
  	  si = i; sj = j;
  	}
  	if(s.at(i).at(j) == 'G'){
  	  gi = i; gj = j;
  	}
  }
  
  const int inf = 1ll << 60;
  vector d(m + 1, vector(h, vector(w, inf)));
  deque<tuple<int, int, int, int>> bfs; // 鍵番号、i、j、距離
  d.at(0).at(si).at(sj) = 0;
  bfs.emplace_back(0, si, sj, 0);
  while(!bfs.empty()){
  	auto [fkey, fi, fj, fd] = bfs.front(); bfs.pop_front();
  	for(auto [di, dj] : vector<pair<int, int>>{{-1, 0}, {0, -1}, {0, 1}, {1, 0}}){
      int tkey = fkey, ti = fi + di, tj = fj + dj, td = fd + 1;
      if(ti < 0 || ti >= h || tj < 0 || tj >= w) continue;
      if(s.at(ti).at(tj) == '#') continue;
      if(islower(s.at(ti).at(tj)) && fkey != s.at(ti).at(tj) - 'a' + 1) continue;
      if(isdigit(s.at(ti).at(tj))) tkey = s.at(ti).at(tj) - '0';
      if(d.at(tkey).at(ti).at(tj) != inf) continue;
      d.at(tkey).at(ti).at(tj) = td;
      bfs.emplace_back(tkey, ti, tj, td);
  	}
  }
  
  int ans = inf;
  rep(i, m + 1) chmin(ans, d.at(i).at(gi).at(gj));
  cout << (ans == inf ? -1ll : ans) << '\n';
}