function M(x: int, b: bool): int 
    decreases !b
{
    if b then x else M(x + 25, true) 
}

function N(x: int, y: int, b: bool): int 
    decreases x, b
{
    if x <= 0 || y <= 0 then
        x + y
    else if b then
        N(x, y + 3, !b)
    else
        N(x - 1, y, true)
}