#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
istream &operator>>(istream &is, modint &a) { long long v; is >> v; a = v; return is; }
ostream &operator<<(ostream &os, const modint &a) { return os << a.val(); }
istream &operator>>(istream &is, modint998244353 &a) { long long v; is >> v; a = v; return is; }
ostream &operator<<(ostream &os, const modint998244353 &a) { return os << a.val(); }
istream &operator>>(istream &is, modint1000000007 &a) { long long v; is >> v; a = v; return is; }
ostream &operator<<(ostream &os, const modint1000000007 &a) { return os << a.val(); } 

typedef long long ll;
typedef vector<vector<int>> Graph;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
#define FOR(i,l,r) for (int i = l;i < (int)(r); i++)
#define rep(i,n) for (int i = 0;i < (int)(n); i++)
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define my_sort(x) sort(x.begin(), x.end())
#define my_max(x) *max_element(all(x))
#define my_min(x) *min_element(all(x))
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
const int INF = (1<<30) - 1;
const ll LINF = (1LL<<62) - 1;
const int MOD = 998244353;
const int MOD2 = 1e9+7;
const double PI = acos(-1);
vector<int> di = {1,0,-1,0};
vector<int> dj = {0,1,0,-1};

#ifdef LOCAL
#  include <debug_print.hpp>
#  define debug(...) debug_print::multi_print(#__VA_ARGS__, __VA_ARGS__)
#else
#  define debug(...) (static_cast<void>(0))
#endif

int main(){
    cin.tie(0);
    ios_base::sync_with_stdio(false);

    int H, W, M;
    cin >> H >> W >> M;
    vector<string> S(H);
    int sx, sy, gx, gy;

    rep(i, H){
        cin >> S[i];
        rep(j, W){
            if(S[i][j] == '.') continue;
            if(S[i][j] == '#') continue;

            if(S[i][j] == 'S'){
                sx = i;
                sy = j;
            }
            if(S[i][j] == 'G'){
                gx = i;
                gy = j;
            }
        }
    }

    vector dist(M + 1, vector(H, vector<int>(W, INF)));
    dist[0][sx][sy] = 0;
    using P = array<int, 3>;
    queue<P> Q;
    Q.push(P{0, sx, sy});

    while(!Q.empty()){
        auto [c, x, y] = Q.front();
        Q.pop();

        rep(d, 4){
            int nx = x + di[d], ny = y + dj[d];
            if(nx < 0 || nx >= H || ny < 0 || ny >= W) continue;
            if(S[nx][ny] == '#') continue;

            if(S[nx][ny] == '.' || S[nx][ny] == 'G'){
                if(dist[c][nx][ny] != INF) continue;

                dist[c][nx][ny] = dist[c][x][y] + 1;
                Q.push(P{c, nx, ny});
            }

            FOR(nc, 1, M + 1){
                if(S[nx][ny] - '0' == nc){
                    if(dist[nc][nx][ny] != INF) continue;

                    dist[nc][nx][ny] = dist[c][x][y] + 1;
                    Q.push(P{nc, nx, ny});
                }
            }

            if(S[nx][ny] - 'a' == c - 1){
                if(dist[c][nx][ny] != INF) continue;

                dist[c][nx][ny] = dist[c][x][y] + 1;
                Q.push(P{c, nx, ny});
            }
        }
    }

    rep(c, M + 1) {
        debug(c);
        debug(dist[c]);
    }


    int ans = INF;
    rep(c, M + 1) chmin(ans, dist[c][gx][gy]);
    cout << (ans < INF ? ans : -1) << endl;
}