with open('data05.txt') as f:
	data = f.readlines()

jumps = list(map(int, data))
steps = 0
i = 0

'''
# part 1
while i < len(jumps):
	old = i
	i += jumps[i]
	jumps[old] += 1
	steps += 1
'''

# part 2
while i < len(jumps):
	j = jumps[i]
	if j > 2:
		jumps[i] -= 1
	else:
		jumps[i] += 1
	i += j
	steps += 1


print(steps)