def oneMoveForward(someBoard):
    length = len(someBoard)
    for x in range(1,someBoard[0]+1):
        if x < length:
            someBoard[x] += 1
        else:
            someBoard.append(1)
    someBoard.pop(0)
    return someBoard

start = input().split()
startBoard = []
for idx in range(len(start)):
    startBoard.append(int(start[idx]))
boards = []
boards.append(startBoard)
repeat = False
count = -1
recursionNum = -1
while repeat == False:
    count += 1
    newBoard = oneMoveForward(boards[count])
    boards.append(newBoard)
    for boardNum in range(len(boards)):
        if newBoard == boards[boardNum]:
            recursionNum = count - boardNum
            repeat ==True
print(recursionNum)