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

using ll = long long;

int main()
{
    cin.tie(nullptr);
    ios::sync_with_stdio(false);

    int H, W, M;
    cin >> H >> W >> M;
    vector<string> grid(H);
    for (int y = 0; y < H; y++)
    {
        cin >> grid[y];
    }

    int startX = 0;
    int startY = 0;
    int endX = 0;
    int endY = 0;
    for (int y = 0; y < H; y++)
    {
        for (int x = 0; x < W; x++)
        {
            if (grid[y][x] == 'S')
            {
                startX = x;
                startY = y;
                grid[y][x] = '.';
            }
            if (grid[y][x] == 'G')
            {
                endX = x;
                endY = y;
                grid[y][x] = '.';
            }
        }
    }

    int layer = H * W;

    vector<bool> seen(layer * (M + 1));
    
    queue<tuple<int, int, int, int>> q;
    q.emplace(startX, startY, 0, 0);
    while (!q.empty())
    {
        auto [x, y, m, d] = q.front();
        q.pop();

        if (x == endX && y == endY)
        {
            cout << d << endl;
            return 0;
        }
        
        if (seen[m * layer + y * W + x]) continue;
        seen[m * layer + y * W + x] = true;

        

        char key = m == 0 ? '@' : (char)('a' + m - 1);

        if (x > 0 && (grid[y][x - 1] == '.' || grid[y][x - 1] == key))
        {
            q.emplace(x - 1, y, m, d + 1);
        }

        if (x < W - 1 && (grid[y][x + 1] == '.' || grid[y][x + 1] == key))
        {
            q.emplace(x + 1, y, m, d + 1);
        }

        if (y > 0 && (grid[y - 1][x] == '.' || grid[y - 1][x] == key))
        {
            q.emplace(x, y - 1, m, d + 1);
        }

        if (y < H - 1 && (grid[y + 1][x] == '.' || grid[y + 1][x] == key))
        {
            q.emplace(x, y + 1, m, d + 1);
        }


        if (x > 0 && isdigit(grid[y][x - 1]))
        {
            q.emplace(x - 1, y, grid[y][x - 1] - '0', d + 1);
        }

        if (x < W - 1 && isdigit(grid[y][x + 1]))
        {
            q.emplace(x + 1, y, grid[y][x + 1] - '0', d + 1);
        }

        if (y > 0 && isdigit(grid[y - 1][x]))
        {
            q.emplace(x, y - 1, grid[y - 1][x] - '0', d + 1);
        }

        if (y < H - 1 && isdigit(grid[y + 1][x]))
        {
            q.emplace(x, y + 1, grid[y + 1][x] - '0', d + 1);
        }
    }

    cout << "-1" << endl;
}