use std::io::Read; fn read() -> T { let token: String = std::io::stdin() .bytes() .map(|c| c.ok().unwrap() as char) .skip_while(|c| c.is_whitespace()) .take_while(|c| !c.is_whitespace()) .collect(); token.parse().ok().unwrap() } mod mint { use std::ops::{Add, Div, Mul, Sub}; type Int = i64; pub const MOD: Int = 1_000_000_000 + 7; #[derive(Clone, Copy)] pub struct Mint { x: Int, } impl Mint { pub fn new(x: Int) -> Mint { Mint { x: (x % MOD + MOD) % MOD, } } pub fn val(&self) -> Int { self.x } } impl Add for Mint { type Output = Mint; fn add(self, rhs: Int) -> Mint { Mint::new(self.val() + (rhs % MOD)) } } impl Add for Mint { type Output = Mint; fn add(self, rhs: Mint) -> Mint { self + rhs.val() } } impl Sub for Mint { type Output = Mint; fn sub(self, rhs: Int) -> Mint { Mint::new(self.val() - (rhs % MOD)) } } impl Sub for Mint { type Output = Mint; fn sub(self, rhs: Mint) -> Mint { self - rhs.val() } } impl Mul for Mint { type Output = Mint; fn mul(self, rhs: Int) -> Mint { Mint::new(self.val() * (rhs % MOD)) } } impl Mul for Mint { type Output = Mint; fn mul(self, rhs: Mint) -> Mint { self * rhs.val() } } impl Mint { pub fn pow(x: Mint, y: Int) -> Mint { assert!(y >= 0); let mut res = Mint::new(1); let mut base = x; let mut exp = y; while exp > 0 { if (exp & 1) == 1 { res = res * base; } base = base * base; exp = exp / 2; } res } pub fn inv(self) -> Mint { Mint::pow(self, MOD - 2) } } impl Div for Mint { type Output = Mint; fn div(self, rhs: Int) -> Mint { self * Mint::new(rhs).inv() } } impl Div for Mint { type Output = Mint; fn div(self, rhs: Mint) -> Mint { self * rhs.val() } } impl std::fmt::Display for Mint { fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result { write!(f, "{}", self.val()) } } } use mint::Mint; struct Cmb { fac: Vec, fac_inv: Vec, } impl Cmb { pub fn new(n: usize) -> Cmb { let mut fac = vec![Mint::new(0); n]; let mut fac_inv = vec![Mint::new(0); n]; fac[0] = Mint::new(1); for i in 1..n { fac[i] = fac[i - 1] * (i as i64); } fac_inv[n - 1] = fac[n - 1].inv(); for i in (0..n - 1).rev() { fac_inv[i] = fac_inv[i + 1] * ((i + 1) as i64) } Cmb { fac, fac_inv } } pub fn binom(&self, a: usize, b: usize) -> Mint { if a < b { return Mint::new(0); } self.fac[a] * self.fac_inv[b] * self.fac_inv[a - b] } } fn main() { let n: usize = read(); let m: usize = read(); let cmb = Cmb::new(m + 2); println!("{}", cmb.binom(m + 1, m - n)); }