number = 0# 0 -> first, 1 -> second
count = 0
NK = [map(int,raw_input().split()) for i in xrange(1000)]
for i in xrange(1000):
	Fwin = False
	mod = NK[i][0] % (NK[i][1] + 1)
	if (mod != 1 and number == 0) or (mod == 1 and number == 1):
		count += 1
		Fwin = True
	if Fwin:
		if(i + 1 < 1000):number = (1 if NK[i + 1][0] % (NK[i + 1][1] + 1) != 1 else 0)
	else:
		if(i + 1 < 1000):number = (0 if NK[i + 1][0] % (NK[i + 1][1] + 1) != 1 else 1)
print count