fn main() {
    const MOD: usize = 1_000_000_007;

    let [n, k]: [usize; 2] = {
        let mut buf = String::new();
        std::io::stdin().read_line(&mut buf).unwrap();
        let mut iter = buf.split_whitespace();
        [
            iter.next().unwrap().parse().unwrap(),
            iter.next().unwrap().parse().unwrap(),
        ]
    };

    let a: Vec<usize> = {
        let mut buf = String::new();
        std::io::stdin().read_line(&mut buf).unwrap();
        let iter = buf.split_whitespace();
        iter.map(|x| x.parse().unwrap()).collect()
    };

    let pow = |mut a, mut n| {
        let mut res = 1;
        while n > 0 {
            if n & 1 > 0 {
                res = res * a % MOD;
            }
            a = a * a % MOD;
            n >>= 1;
        }
        res
    };

    let mut c = Vec::with_capacity(n);
    c.push(1);
    for i in 1..n {
        c.push(c[i - 1] * (k + i) % MOD * pow(i, MOD - 2) % MOD);
    }

    let mut ans = 0;
    for i in 0..n {
        ans = (ans + c[i] * c[n - 1 - i] % MOD * a[i] % MOD) % MOD;
    }
    println!("{}", ans);
}