n,k = map(int,input().split())

if n%2:
    if k%2:
        l1 = 2
        r1 = min(1+k,n-1)
        r2 = n
        l2 = max(1,n-k+1)
    else:
        l1 = 1
        r1 = min(n,1+k)
        r2 = n-1
        l2 = max(2,n-k+1)


    ans = (r1-l1)//2+(r2-l2)//2+2
else:

    if k%2:
        l1 = 2
        r1 = min(1+k,n)
        r2 = n
        l2 = max(2,n-k+1)
    else:
        l1 = 1
        r1 = min(n-1,1+k)
        r2 = n-1
        l2 = max(1,n-k+1)

    if r1 <= l2:
        ans = (r2-l1)//2+1
    else:
        ans = (r1-l1)//2+(r2-l2)//2+2
print(ans)