# BFS
    path={}
    for x in ladders+snakes:
        path[x[0]]=x[1]

    qu=[(1,0)]
    visit=set({1})
    while len(qu)>0:
        cur,step=qu.pop(0)
        if cur>=100:
            return step
        for i in range(1,7):
            if cur+i in path:
                nxt=path[cur+i]
            else:
                nxt=cur+i
            if nxt not in visit:
                visit.add(nxt)
                qu.append((nxt,step+1))
    
    return -1