number = 0# 0 -> first, 1 -> second
count = 0
N,K = [],[]
for i in range(1000):
	n,k = map(int,raw_input().split())
	N.append(n)
	K.append(k)
for i in range(1000):
	Fwin = False
	mod = N[i] % (K[i] + 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 N[i + 1] % (K[i + 1] + 1) != 1 else 0)
	else:
		if(i + 1 < 1000):number = (0 if N[i + 1] % (K[i + 1] + 1) != 1 else 1)
print count