def solve():
    from collections import deque

    H, W, M = map(int, input().split())

    dist = [[[-1] * (M + 1) for _ in range(W)] for _1 in range(H)]
    S = [None] * H
    for i in range(H):
        S[i] = input()
        for j in range(W):
            if S[i][j] == "S":
                start = (i, j)
            elif S[i][j] == "G":
                goal = (i, j)

    Q = deque([(start, 0)])
    dist[start[0]][start[1]][0] = 0
    while Q:
        p, key = Q.popleft()
        i, j = p
        d = dist[i][j][key]
        for di, dj in [(1, 0), (-1, 0), (0, 1), (0, -1)]:
            qi = i + di
            qj = j + dj

            if not(0 <= qi < H and 0 <= qj < W):
                continue

            if S[qi][qj] == "." or S[qi][qj] == "G" or S[qi][qj] == "S":
                if dist[qi][qj][key] == -1:
                    Q.append(((qi, qj), key))
                    dist[qi][qj][key] = d + 1
                if S[qi][qj] == "G":
                    return dist[qi][qj][key]
            elif "1" <= S[qi][qj] <= "9":
                k = int(S[qi][qj])
                if dist[qi][qj][k] == -1:
                    Q.append(((qi, qj), k))
                    dist[qi][qj][k] = d + 1
            elif "a" <= S[qi][qj] <= "i":
                if chr(key + ord("a") - 1) == S[qi][qj] and dist[qi][qj][key] == -1:
                    Q.append(((qi, qj), key))
                    dist[qi][qj][key] = d + 1
    return -1

#==================================================
print(solve())