import sys def day5_2(input): maze = list(map(lambda x: int(x.rstrip()), input.split())) size = len(maze) steps = 0 pc = 0 while pc >= 0 and pc < size: offset = maze[pc] if offset >= 3: maze[pc] -= 1 else: maze[pc] += 1 pc += offset steps += 1 return "%d" % steps input = sys.stdin.read() print(day5_2(input))