from collections import deque

ways = [(-1, 0), (1, 0), (0, -1), (0, 1)]


def solve():
    H, W, M = map(int, input().split())
    grid = [list(input()) for _ in range(H)]

    s_i, s_j = None, None
    for i in range(H):
        for j in range(W):
            if grid[i][j] == "S":
                s_i, s_j = i, j
                break
        else:
            continue
        break

    visited = [[[False] * W for _ in range(H)] for _ in range(M + 1)]
    visited[0][s_i][s_j] = True

    que = deque([(s_i, s_j, 0, 0)])

    while que:
        curr_i, curr_j, key, dist = que.popleft()

        for di, dj in ways:
            next_i, next_j = curr_i + di, curr_j + dj

            if not (0 <= next_i < H and 0 <= next_j < W):
                continue

            if grid[next_i][next_j] == "#":
                continue

            if grid[next_i][next_j].islower() and grid[next_i][next_j] != chr(ord("a") + key - 1):
                continue

            if grid[next_i][next_j] == "G":
                print(dist + 1)
                return

            if grid[next_i][next_j].isdigit():
                next_key = int(grid[next_i][next_j])

                if not visited[next_key][next_i][next_j]:
                    que.append((next_i, next_j, next_key, dist + 1))
                    visited[next_key][next_i][next_j] = True
            else:
                if not visited[key][next_i][next_j]:
                    que.append((next_i, next_j, key, dist + 1))
                    visited[key][next_i][next_j] = True

    print(-1)


if __name__ == "__main__":
    solve()