#include <bits/stdc++.h>
using namespace std;

#define For(i, a, b) for(int i = (a); i < (b); i++)
#define rep(i, n) For(i, 0, n)
#define rFor(i, a, b) for(int i = (a); i >= (b); i--)
#define ALL(v) (v).begin(), (v).end()
#define rALL(v) (v).rbegin(), (v).rend()
#define SZ(v) ((int)(v).size())

using lint = long long;
using ld = long double;

int INF = 2000000000;
lint LINF = 1000000000000000000;

struct SetupIo {
    SetupIo() {
        ios::sync_with_stdio(false);
        cin.tie(nullptr);
        cout << fixed << setprecision(15);
        cerr << fixed << setprecision(15);
    }
} setupio;

// a <- max(a, b)
template <class T>
bool chmax(T &a, const T &b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
}

// a <- min(a, b)
template <class T>
bool chmin(T &a, const T &b) {
    if (a > b) {
        a = b;
        return true;
    }
    return false;
}

vector<int> di = {0, 0, -1, 1};
vector<int> dj = {-1, 1, 0, 0};

int main() {
    int H, W, M;
    cin >> H >> W >> M;
    vector<vector<char>> S(H, vector<char>(W));
    int si, sj, gi, gj;
    rep(i, H) {
        rep(j, W) {
            cin >> S[i][j];
            if (S[i][j] == 'S') {
                si = i;
                sj = j;
            }
            if (S[i][j] == 'G') {
                gi = i;
                gj = j;
            }
        }
    }
    auto inside = [&](int i, int j) -> bool {
        return (0 <= i && i < H && 0 <= j && j < W);
    };
    // dist[i][j][k]:= 鍵 k を持った状態で (i, j) に到達
    vector<vector<vector<int>>> dist(H, vector<vector<int>>(W, vector<int>(M + 1, INF)));
    queue<tuple<int, int, int>> q;
    dist[si][sj][0] = 0;
    q.emplace(si, sj, 0);
    while (!q.empty()) {
        auto [i, j, k] = q.front();
        q.pop();
        rep(kk, 4) {
            int ni = i + di[kk], nj = j + dj[kk];
            if (!inside(ni, nj) || S[ni][nj] == '#') {
                continue;
            }
            if (S[ni][nj] == '.' || S[ni][nj] == 'S' || S[ni][nj] == 'G') {
                int nk = k;
                if (chmin(dist[ni][nj][nk], dist[i][j][k] + 1)) {
                    q.emplace(ni, nj, nk);
                }
            } else if ('1' <= S[ni][nj] && S[ni][nj] <= '9') {
                int nk = S[ni][nj] - '0';
                if (chmin(dist[ni][nj][nk], dist[i][j][k] + 1)) {
                    q.emplace(ni, nj, nk);
                }
            } else {
                int x = S[ni][nj] - 'a' + 1;
                if (k == x) {
                    int nk = k;
                    if (chmin(dist[ni][nj][nk], dist[i][j][k] + 1)) {
                        q.emplace(ni, nj, nk);
                    }
                }
            }
        }
    }
    int ans = INF;
    rep(k, M + 1) {
        chmin(ans, dist[gi][gj][k]);
    }
    cout << (ans != INF ? ans : -1) << "\n";
}