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

S = [0] * H
for i in range(H):
    S[i] = input()

INF = 10 ** 9
for i in range(H):
    for j in range(W):
        if S[i][j] == "S":
            x = i
            y = j

q = [(0, x, y, 0)]
v = [[[INF] * (M+1) for i in range(W)] for j in range(H)]
v[x][y][0] = 0

def f(x):
    return ord(x) - ord("a") + 1

from collections import deque

q = deque(q)

dx = [1, -1, 0, 0]
dy = [0, 0, 1, -1]

ans = INF
while q:
    d, x, y, a = q.popleft()

    for k in range(4):
        nx = x + dx[k]
        ny = y + dy[k]

        if nx < 0 or H <= nx or ny < 0 or W <= ny:
            continue

        if S[nx][ny] in "S." and v[nx][ny][a] == INF:
            q.append((d+1, nx, ny, a))
            v[nx][ny][a] = d+1
        elif S[nx][ny].isnumeric():
            b = int(S[nx][ny])
            if v[nx][ny][b] == INF:
                q.append((d+1, nx, ny, b))
                v[nx][ny][b] = d+1

        elif S[nx][ny] in "#":
            continue
        elif S[nx][ny] == "G":
            ans = min(ans, d+1)
        else:
            if a == f(S[nx][ny]) and v[nx][ny][a] == INF:
                q.append((d+1, nx, ny, a))
                v[nx][ny][a] = d+1
                   

if ans == INF:
    print(-1)
else:
    print(ans)