T = 1000
f = True
ans = 0
for t in range(T):
    n, k = map(int, input().split())
    x = (n-1) % (k+1) != 0
    if f:
        if x:
            ans += 1
            f = False
        else:
            f = True
    else:
        if not x:
            ans += 1
            f = False
        else:
            f = True

print(ans)