import sys
sys.setrecursionlimit(10**7)
def input():
    return sys.stdin.readline().strip()

from collections import deque
def main():
    H, W, M = map(int, input().split())
    S = [input() for _ in range(H)]
    DOOR = [None] * M
    for i, line in enumerate(S):
        for j, cell in enumerate(line):
            if cell == 'S':
                START = W * i + j
            elif cell == 'G':
                GOAL = W * i + j
    DIRS = ((1, 0), (0, 1), (-1, 0), (0, -1))

    INF = 10**8
    dist = [[INF] * (M+1) for _ in range(H*W)]
    dist[START][0] = 0
    queue = deque([(START, 0)])

    while queue:
        c, k = queue.popleft()
        i, j = divmod(c, W)
        for di, dj in DIRS:
            ni = i + di
            nj = j + dj
            nc = W * ni + nj
            if 0 <= ni < H and 0 <= nj < W:
                if S[ni][nj] in ('.', 'S', 'G') and dist[nc][k] == INF:
                    queue.append((nc, k))
                    dist[nc][k] = dist[c][k] + 1
                elif S[ni][nj].isdigit() and dist[nc][int(S[ni][nj])] == INF:
                    queue.append((nc, int(S[ni][nj])))
                    dist[nc][int(S[ni][nj])] = dist[c][k] + 1
                elif ord('a') <= ord(S[ni][nj]) <= ord('z') and k == ord(S[ni][nj]) - ord('a') + 1 and dist[nc][k] == INF:
                    queue.append((nc, k))
                    dist[nc][k] = dist[c][k] + 1

    ans = min(dist[GOAL])
    print(ans) if ans < INF else print(-1)


if __name__ == '__main__':
    main()