ms = 0
gs = 0

first = "m"
for i in range(1000):
    n, k = map(int,input().split())
    if (n-1)%(k+1) != 0:
        if first == "m":
            ms += 1
            first = "g"
        else:
            gs += 1
            first = "m"
    else:
        if first == "m":
            gs += 1
            first ="m"
        else:
            ms += 1
            first = "g"
print(ms)