const MOD: usize = 1e9 as usize + 7;

fn main() {
    let mut a = String::new();
    std::io::stdin().read_line(&mut a).ok();
    let a: usize = a.trim().parse().unwrap();
    let mut b = String::new();
    std::io::stdin().read_line(&mut b).ok();
    let mut b = b.trim().chars().map(|c| c as usize - '0' as usize).collect::<Vec<_>>();

    b.reverse();
    let mut result = 0usize;
    let mut rank = 1usize;
    let mut current = 1usize;
    for i in 0..b.len()-1 {
        result += (rank * a - rank) * i % MOD;
        result %= MOD;
        current += rank * b[i] % MOD;
        current %= MOD;
        rank *= a;
        rank %= MOD;
    }
    result += (current + (b[b.len()-1] - 1) * rank) * (b.len()-1) % MOD;
    result %= MOD;
    println!("{}", result);
}