#include <bits/stdc++.h>
#include <atcoder/all>
#include <boost/multiprecision/cpp_dec_float.hpp>
#include <boost/multiprecision/cpp_int.hpp>
namespace mp = boost::multiprecision;
using Bint = mp::cpp_int;
using namespace std;
using namespace atcoder;
#define rep(i, n) for(int i=0;i<(n);++i)
#define rep1(i, n) for(int i=1;i<=(n);i++)
#define ll long long
using mint = modint998244353;
using P = pair<ll,ll>;
using lb = long double;
using T = tuple<ll, ll, ll>;
#ifdef LOCAL
#  include <debug_print.hpp>
#  define dbg(...) debug_print::multi_print(#__VA_ARGS__, __VA_ARGS__)
#else
#  define dbg(...) (static_cast<void>(0))
#endif

int main()
{
    int h, w, m;
    cin >> h >> w >> m;
    vector<string> s(h);
    rep(i,h) cin >> s[i];
    const int INF = 1e9;
    vector<vector<vector<int>>> dist(h, vector<vector<int>>(w, vector<int>(m+1, INF)));
    queue<tuple<int, int, int>> q;
    rep(i,h)rep(j,w) {
        if(s[i][j]=='S') {
            dist[i][j][0] = 0;
            q.emplace(i,j,0);
        }
    }
    vector<int> di = {0, -1, 0, 1};
    vector<int> dj = {-1, 0, 1, 0};
    while(!q.empty()) {
        auto [i,j,k] = q.front();q.pop();
        dbg(i,j,k);
        rep(d,4) {
            int ni = i + di[d];
            int nj = j + dj[d];
            int nk = k;
            if(ni<0 || ni>=h || nj<0 || nj>=w) continue;
            if(s[ni][nj]=='#') continue;
            if(s[ni][nj]=='.' || s[ni][nj]=='G' || s[ni][nj]=='S') {
                
            } 
            else if(s[ni][nj]>='1' && s[ni][nj]<='9') {
                nk = s[ni][nj] - '0';
            }
            else{
                if(s[ni][nj]-'a'!=k-1) continue;
            }
            if(dist[ni][nj][nk]>dist[i][j][k]+1) {
                dbg(nk,s[ni][nj]);
                dist[ni][nj][nk] = dist[i][j][k]+1;
                q.emplace(ni,nj,nk);
            }
        }
    }
    int ans = INF;
    rep(i,h)rep(j,w) {
        if(s[i][j]=='G') {
            rep(k,m+1) ans = min(ans, dist[i][j][k]);
        }
    }
    if(ans==INF) ans = -1;
    cout << ans << endl;
    return 0;
}