#[allow(unused_imports)]
use std::cmp::{Ordering};

#[allow(unused_imports)]
use std::collections::{BTreeMap, BTreeSet, BinaryHeap, HashMap, HashSet, VecDeque};

#[allow(unused_imports)]
use std::io::{stdin, stdout, BufWriter, Write};

#[allow(unused_imports)]
use std::iter::FromIterator;

#[allow(unused_macros)]
macro_rules! min {
    ($x: expr) => ($x);
    ($x: expr, $($z: expr),+) => {{
        std::cmp::min($x, min!($($z),*))
    }}
}

#[allow(unused_macros)]
macro_rules! max {
    ($x: expr) => ($x);
    ($x: expr, $($z: expr),+) => {{
        std::cmp::max($x, max!($($z),*))
    }}
}

#[allow(unused_macros)]
macro_rules! get { 
    ([$t: ty]) => { 
        { 
            let mut line = String::new(); 
            stdin().read_line(&mut line).unwrap(); 
            line.split_whitespace().map(|t|t.parse::<$t>().unwrap()).collect::<Vec<_>>()
        }
    };
    ([$t: ty];$n: expr) => {
        (0..$n).map(|_|get!([$t])).collect::<Vec<_>>()
    };
    ($t: ty) => {
        {
            let mut line = String::new();
            stdin().read_line(&mut line).unwrap();
            line.trim().parse::<$t>().unwrap()
        }
    };
    ($($t: ty),*) => {
        { 
            let mut line = String::new();
            stdin().read_line(&mut line).unwrap();
            let mut iter = line.split_whitespace();
            ($(iter.next().unwrap().parse::<$t>().unwrap(),)*)
        }
    };
    ($t: ty; $n: expr) => {
        (0..$n).map(|_|get!($t)).collect::<Vec<_>>()
    };
    ($($t: ty),*; $n: expr) => {
        (0..$n).map(|_|get!($($t),*)).collect::<Vec<_>>()
    };
}

#[allow(unused_macros)]
macro_rules! debug {
    ($($a:expr),*) => {
        #[cfg(debug_assertions)]
        writeln!(&mut std::io::stderr(), concat!("[DEBUG] ", $(stringify!($a), "={:?} "),*), $($a),*).unwrap();
    }
}

const BIG_STACK_SIZE: bool = true;

#[allow(dead_code)]
fn main() {
    use std::thread;
    if BIG_STACK_SIZE {
        thread::Builder::new()
            .stack_size(32 * 1024 * 1024)
            .name("solve".into())
            .spawn(solve)
            .unwrap()
            .join()
            .unwrap();
    } else {
        solve();
    }
}

#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]
struct ModInt {
    value: usize,
}

impl ModInt {
    fn new(value: usize) -> Self {
        ModInt {
            value: value % Self::modulo(),
        }
    }

    fn value(&self) -> usize {
        self.value
    }

    fn modulo() -> usize {
        1_000_000_007
    }
}

impl From<usize> for ModInt {
    fn from(value: usize) -> Self {
        ModInt {
            value: value,
        }
    }
}

impl std::ops::Add for ModInt {
    type Output = Self;

    fn add(self, other: Self) -> Self {
        let mut value = self.value + other.value;
        if value > Self::modulo() {
            value -= Self::modulo();
        }
        ModInt {
            value: value,
        }
    }
}

impl std::ops::Sub for ModInt {
    type Output = Self;

    fn sub(self, other: Self) -> Self {
        let mut value = self.value;
        if value < other.value {
            value += Self::modulo();
        }
        value -= other.value;
        ModInt{
            value: value,
        }
    }
}

impl std::ops::Mul for ModInt {
    type Output = Self;

    fn mul(self, other: Self) -> Self {
        let value = self.value * other.value % Self::modulo();
        ModInt {
            value: value,
        }
    }
}

impl std::ops::Div for ModInt {
    type Output = Self;

    fn div(self, other: Self) -> Self {
        let mut exp = Self::modulo()-2;
        let mut value = self.value;
        let mut ovalue = other.value;
        while exp > 0 {
            if exp % 2 == 1 {
                value = value * ovalue % Self::modulo();
            }
            ovalue = ovalue * ovalue % Self::modulo();
            exp /= 2;
        }
        ModInt {
            value: value,
        }
    }
}

impl std::fmt::Debug for ModInt {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        write!(f, "{}", self.value)
    }
}

impl std::fmt::Display for ModInt {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        write!(f, "{}", self.value)
    }
}

fn fact(n: ModInt) -> ModInt {
    (1..n.value()+1).fold(ModInt::new(1), |mul, e| mul*ModInt::new(e))
}

fn solve() {
    let (n, m) = get!(usize, usize);

    if n + 1 < m  || m + 1 < n {
        println!("0");
        return;
    }
    let n = ModInt::new(n);
    let m = ModInt::new(m);

    let res = if n == m {
        ModInt::new(2) * fact(n) * fact(m)
    } else {
        fact(n) * fact(m)
    };

    println!("{}", res);
}


Measured memory_bytes: 8572