from collections import deque
H,W,M=map(int,input().split())
S=[input() for _ in range(H)]
for h in range(H):
    for w in range(W):
        if S[h][w]=="S":s=(h,w)
        elif S[h][w]=="G":g=(h,w)
vis=set()
Q=deque([(s,0,0)])
while Q:
    (h,w),cnt,key=Q.popleft()
    vis.add((h,w))
    if (h,w)==g:exit(print(cnt))
    if "1"<=S[h][w]<="9":key=int(S[h][w])
    for dh,dw in ((-1,0),(1,0),(0,-1),(0,1)):
        if not (0<=h+dh<H and 0<=w+dw<W):continue
        if S[h+dh][w+dw]=="#":continue
        if (h+dh,w+dw) in vis:continue
        if "a"<=S[h+dh][w+dw]<="i" and ord(S[h+dh][w+dw])-ord("a")+1!=key:continue
        Q.append(((h+dh,w+dw),cnt+1,key))
print(-1)