// https://yukicoder.me/problems/no/1275

use proconio::input;

use std::i64;

const MOD:i64 = 1000000007;

fn prod(left: &[[i64;2];2], right : &[[i64;2];2]) -> [[i64;2]; 2] {
    let mut new_matrix = [[0, 0], [0, 0]];
    for i in 0..2 {
        for j in 0..2 {
            for k in 0..2{
                new_matrix[i][j] += (left[i][k] * right[k][j]) % MOD;
                new_matrix[i][j] %= MOD
            }
        }
    }
    return new_matrix;
}

fn main() {
    input! {
        a: i64,
        b: i64,
        n: i64,
    }

    //  (a + sqrt(b))^n について計算する
    let mut base_matrix = [[a, b], [1, a]];
    let mut ans_matrix = [[1, 0], [0, 1]];
    let mut n1 = n;
    while n1 > 0 {
        if n1 % 2 == 1 {
            ans_matrix = prod(&base_matrix, &ans_matrix);
        }

        base_matrix = prod(&base_matrix, &base_matrix);
        n1 /= 2;
    }
    let a1 = ans_matrix[0][0];

    //  (a - sqrt(b))^n について計算する
    let mut base_matrix2= [[a, -b], [-1, a]];
    let mut ans_matrix2 = [[1, 0], [0, 1]];
    let mut n2 = n;
    while n2 > 0 {
        if n2 % 2 == 1 {
            ans_matrix2 = prod(&base_matrix2, &ans_matrix2);
        }

        base_matrix2 = prod(&base_matrix2, &base_matrix2);
        n2 /= 2;
    }
    let a2 = ans_matrix2[0][0];

    let answer = (a1 + a2) % MOD;
    println!("{}", answer);




}