measures = [int(i) for i in open("input.txt", 'r').read().splitlines()]

increases = 0
old = measures[0]+measures[1]+measures[2] 
for i in range(3,len(measures)):
	new = measures[i] + measures[i-1] + measures[i-2]
	if new > old:
		increases += 1
	old = new

print(increases)